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Characteristics of the Changxing Fm biohermal gas reservoir in the Yuanba Gasfield, Sichuan Basin and development countermeasures
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ScienceDirect Natural Gas Industry B 3 (2016) 537e544 www.elsevier.com/locate/ngib
Research Article
Characteristics of the Changxing Fm biohermal gas reservoir in the Yuanba Gasfield, Sichuan Basin and development countermeasures* Wu Hengzhi a, Li Zhongping a, Ke Guangming b,* b
a Sinopec Southwest Branch Company, Chengdu, Sichuan 610081, China Exploration and Development Research Institute, Sinopec Southwest Branch Company, Chengdu, Sichuan 610081, China
Received 8 July 2016; accepted 25 September 2016 Available online 23 June 2017
Abstract Located in the Sichuan Basin, the Yuanba Gasfield is the deepest high-sulfur carbonate gas field among those discovered in the world. Its biohermal gas reservoir of the Upper Permian Changxing Fm is characterized by ultra depth, multi-stage small and scattered reef, thin reservoir, poor physical properties, strong heterogeneity, complex fluid distribution, and low production of vertical wells. The development of the biohermal gas reservoir is subject to many difficulties. For example, it is necessary to deepen the studies on timeespace distribution laws of reef dolomite reservoirs; it is difficult to characterize small reefs precisely and predict thin reservoirs quantitatively; the deployment and optimization design of horizontal wells are influenced by multiple factors; and the difficulty for horizontal wells with long horizontal sections to run through high-quality thin reservoirs is high. In order to develop the Yuanba Gasfield efficiently, therefore, it is necessary to carry out a series of technical researches on the distribution laws and development models of biohermal reservoirs, precise characterization of small reefs, quantitative prediction of thin reservoirs, optimization design of horizontal wells in banded small reef gas reservoirs, and real-time trajectory optimization and adjustment of horizontal wells in ultra-deep thin reservoirs. These research results provide a powerful support for the development and construction of the Yuanba Gasfield. Based on these technologies, China's first ultra-deep high-sulfur large biohermal gas field was built with a mixed gas annual production capacity of 40 108 m3. The successful commissioning of the Yuanba Gasfield lays a basis for the leading position of China in the field of high-sulfur gas field development. In addition, it is of great significance to the long-term stable gas supply in 70 cities of six provinces and two municipalities along the “Sichuan-to-East China Gas Transmission Pipeline”, as well as to the industrial structure adjustment in centralewestern China and the economic development along the Yangtze River. © 2017 Sichuan Petroleum Administration. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Keywords: Sichuan Basin; Yuanba Gasfield; Late permian; Biohermal gas reservoir; Reservoir; Development model; Reef characterization; Horizontal well design; Trajectory optimization
The Yuanba Gasfield is the deepest carbonate gas field with high sulfur content ever discovered around the world. Gas accumulations in the Upper Permian Changxing Fm mainly occur in marginal platform dolomite of organic reef and bank facies. More and more gas reservoirs with high sulfur content * Project supported by the National Science and Technology Major Project in the 13th Five-Year Plan “High-efficiency development of ultra-deep bioherm gas reservoirs with bottom water” (No.: 2016ZX05017-005). * Corresponding author. E-mail address: [email protected] (Ke GM.). Peer review under responsibility of Sichuan Petroleum Administration.
have been discovered in China and abroad [1e3]. The development of such reservoirs is among the major national energy strategies for promoting gas industry and technical research in China. But commercial production is challenging and there are no successful cases for Ref. [4]. In this paper, reservoir distribution, quantitative prediction of small reefs and thin reservoirs, horizontal well design for belt-like small biohermal gas reservoirs, and real-time adjustment of horizontal wellbore track through ultra-deep thin reservoirs are discussed, followed by the analyses of possible strategies on high-efficiency gas reservoir development.
http://dx.doi.org/10.1016/j.ngib.2017.05.003 2352-8540/© 2017 Sichuan Petroleum Administration. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
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1. Gas reservoir geological features The Changxing Fm biohermal gas reservoir in the Yuanba Gasfield features large burial depth, small size, scattered distribution, small thickness, poor petrophysical properties, strong heterogeneity, complex fluid distribution, and low vertical-well production.
and 0.250 mD and above 1 mD (Fig. 1). The wide span of permeability indicates strong heterogeneity. As per log interpretation of 23 wells, the porosity of Changxing Fm reeffacies reservoirs ranges from 2.0% to 14.2% (Fig. 2), with an average of 4.8%. The permeability ranges from 0.01 to 13483.89 mD, with a geometric average of 0.99 mD. In general, the Changxing Fm reservoir is of low porosity and medium to low permeability.
1.1. Ultra-deep reservoirs Tectonically, the Yuanba Gasfield lies at the joint of the northern Sichuan depression and central Sichuan gentle structural belt in the Sichuan Basin. The Changxing Fm presents a NE-inclined monoclinal structure. Its average burial depth exceeds 6600 m (the top and bottom of the Changxing Fm were drilled at 6239e7244 m). Among deep reservoirs in China for exploration and development in recent years [5e10], the Changxing Fm gas reservoir in the Yuanba field is the deepest one for commercial production. The Changxing Fm gas reservoir is 700e1500 m deeper than the Longgang gas field, 800e1500 m deeper than the Puguang field, 2600 m deeper than the Wubaiti field, and 3200e3700 m deeper than the Tieshan field. 1.2. Multi-phase small scattered reefs As per well drilling and seismic data, the Yuanba Gasfield was on the marginal gentle-slope platform on the west side of the KaijiangeLiangping shelf during the Changxing Fm deposition [11e13]. The degree of slope was 8 e10 [14e17]. In such an environment with relatively weak hydrodynamic conditions, organic reefs grew slowly in the form of vertical accretion and lateral migration. As a result, many late reefs are superimposed upon early reefs and scatter laterally in a wide area; a single reef is small in size. Flood [18]made a study of bioherm limestone deposited in the Heron Island in 1993. They found that reef-bank deposits on the marginal gentleslope platform nowadays have similar features, i.e. small single reef size, multi-phase stacking of reefs in vertical direction, and scattered distribution in lateral direction. As per the studies made by Ma et al. [16], Wang et al. [17], Guo [19], and Zhao et al. [20]. On the temporalespatial configuration of the Changxing Fm marginal platform reef-bank system, multiphase organic reefs exist in the Yuanba Gasfield and migrate laterally in different directions. 1.3. Strong heterogeneity 1.3.1. Poor reservoir properties Analysis of 465 core samples acquired from 16 wells shows that the porosity of the Changxing Fm reef-facies reservoirs in the Yuanba Gasfield ranges from 0.53% to 23.59%, with an average of 4.87%. Samples with a porosity above 2% average at 5.76%. About 47% of the total samples have a porosity of 2e5%. About 21% of the total samples have a porosity below 2% and between 5% and 10%. The permeability ranges from 0.0007 to 1720.7190 mD, with a geometric average of 0.5111 mD. Most samples have a permeability between 0.002
1.3.2. Small reservoir thickness. In the Yuanba Gasfield, the average thickness of reef-facies reservoirs in 23 wells is 58.8 m. Grade I gas layers are 0e15.8 m thick with an average of 2.66 m and account for 4.72% of the total reservoir thickness. Grade II gas layers are 0e56.3 m thick with an average of 18.5 m and account for 32.85% of the total reservoir thickness. Grade III gas layers are 2.1e67.3 m thick with an average of 25.8 m and account for 45.83% of the total reservoir thickness. Gas-bearing layers are 0e20.8 m thick with an average of 2.21% and account for 3.92% of the total reservoir thickness. Gasewater layers are 0e34.65 m thick with an average of 2.72 m and account for 4.82% of the total reservoir thickness. Water layers with low gas saturation are 0e59.6 m with an average of 4.05 m and account for 7.19% of the total reservoir thickness. Water layers are 0e8.45 m thick with an average of 0.37 m and account for 0.65% of the total reservoir thickness (Fig. 3). 1.3.3. Strong heterogeneity As per reservoir correlation, the Changxing Fm reservoir of reef and bank facies exhibits strong heterogeneity both in vertical and lateral directions. Generally speaking, different types of reservoirs have different thickness and may not be connected laterally; reservoir thickness also changes greatly in lateral direction (Fig. 4). 1.4. Complex gasewater distribution As per log interpretation and testing results, it is inferred that the Changxing Fm gas reservoir in the Yuanba Gasfield exists in a separate reef and has relatively isolated gasewater system. There are no regional water bodies which occur as edge water or bottom water. Studies show that gasewater distribution in reservoirs of reef facies in No. 2, No. 3 and No. 4 reef fairways is obviously dominated by present structures. Generally, the wells drilled at the structural lows produced water, especially in YB273, YB28 and YB103H wells. But in No. 1 reef fairway, there is no remarkable relationship between gasewater production and structural location. Wells YB9, YB107 and YB10-1H all produced water with different volumes (Fig. 5). 1.5. Low vertical-well productivity As per the testing results of 15 wells, vertical wells drilled in the Yuanba Gasfield have low productivity of Changxing Fm biohermal gas. Openflow capacity was tested to range at (7e318) 104 m3/d and the average was 149 104 m3/d.
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Fig. 1. Porosity and permeability histograms based on core data of Changxing Fm reef-facies reservoir in the Yuanba Gasfield.
2. Challenges to commercial gas production In view of complex gas reservoir geological features, it is hard to delineate biohermal reservoir distribution, predict small reefs and thin reservoirs, deploy and optimize development wells, and adjust wellbore track in real time. The challenges are detailed as follows. (1) The Changxing Fm organic reefs formed in multi-period in the Yuanba Gasfield are small in size and scatter throughout the marginal gentleslope platform. Besides, reservoir rocks are highly heterogeneous. Thus it is necessary to deepen the understanding of temporalespatial reservoir distribution. (2) Due to ultragreat burial depth of the intervals being investigated, seismic signals are of weak energy and low signal-to-noise ratio and resolution [21,22], which makes it difficult to quantitatively predict small reefs and thin reservoirs. (3) It is hard to realize profitable production via vertical wells. The deployment and optimization of horizontal wells in small reefs and thin reservoirs are dependent on many factors. (4) It is hard to laterally penetrate a high-graded thin reservoir bed of 1000 m buried at nearly 7000 m through horizontal well drilling. 3. Development countermeasures 3.1. Biohermal reservoir distribution law and dolomitization models 3.1.1. Major controlling factors for reef-facies dolomite reservoirs Studies [23,24] show that the formation of organic reefs is greatly dependent on ancient land forms at the depositional
stage. In the Yuanba Gasfield, organic reefs are most likely to occur at the structural highs of the marginal platform, slope break belt, and intra-platform highland [25]. The Changxing Fm reservoir rocks with good properties in the Yuanba Gasfield are mainly organic reefs on the marginal platform. Lateral reservoir distribution is related to sedimentary microfacies. Vertical reservoir distribution is dominated by high-frequency cycles at the depositional stage. Reservoir rocks concentrate in the middle and upper parts of the descending hemicycle in the fourth order sequence; this is because early native rocks tended to be dolomitized due to sea level drop during deposition in the descending hemicycle in the fourth order sequence [26e28]. For organic reefs on the marginal platform, reservoir variations in lateral and vertical directions are related to differential diageneses, which gave rise to a strong heterogeneity of reef-facies dolomite reservoirs. The evolution of dolomite reservoirs in the Yuanba Gasfield is dependent on dolomitization and chemical erosion. Contemporaneous high-salinity dolomitization and medium-term shallow-burial dolomitization gave birth to dolomite, which was corroded by organic acids and sulfates at the middle and late stages to form pore space for the Changxing Fm gas accumulation. A single organic reef is vertically subdivided into reef base, reef core and reef cap and laterally subdivided into reef front, reef crest and back reef. The reef crest (reef cap) experienced early evaporative pumping dolomitization, shallow-burial dolomitization, and intense middle and late chemical erosion and thus has the best reservoir rocks. The back reef experienced early reflux permeation dolomitization, shallow-burial dolomitization, and intense middle and late chemical erosion and also has good reservoir rocks (Fig. 6).
Fig. 2. Average porosity histograms based on log interpretation of Changxing Fm reef-facies reservoirs in the Yuanba Gasfield.
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Fig. 3. Thickness histograms based on log interpretation of Changxing Fm reef-facies reservoir in the Yuanba Gasfield.
3.1.2. Reef-facies reservoir distribution law The Changxing Fm organic reefs in the Yuanba Gasfield may form in a single phase or two phases (Fig. 7). Vertically, a single-phase reef reservoir mainly occurs at the cap (with an average thickness of 39.9 m); two-phase reservoirs mainly occur at the upper phase-II cap (with an average thickness of 42.9 m) and some occur at the lower phase-I cap (with an average thickness of 21.6 m). Laterally, reef reservoirs mainly distribute at the crest (the average thickness is 77.0 m; the average thickness of Grade I þ II layers is 37.0 m) and some distribute at the back reef (the average thickness is 38.3 m; the average thickness of Grade I þ II layers is 11.0 m). Some thin reservoirs exist at the reef front (the average thickness is 32.6 m; the average thickness of Grade I þ II layers is 9.5 m). 3.1.3. Reef cluster development and reservoir distribution models The Changxing Fm organic reefs in the Yuanba Gasfield were deposited on the marginal gentle-slope platform. Due to ancient land forms at the depositional stage and frequent sea level changes, organic reefs formed in multi-period feature small size and scattered distribution. Complex occurrences of organic reefs and reef-facies reservoirs make it difficult to optimize the deployment of development wells and wellbore track. After comprehensive analyses of bioherm stratigraphic features and seismic reflection configurations, reef clusters and reef-facies reservoirs with 5 models were described, i.e. vertical progradation (A), vertical retrogradation (B), lateral juxtaposition (C), lateral migration (D), and superposition (E)
(Fig. 7). These models would be used in reef identification, quantitative reservoir prediction, development well deployment, and wellbore track optimization. 3.2. Fine reef description and quantitative reservoir prediction 3.2.1. Ultra-deep small reef identification and description Reef models were used to guide reef identification. Reef fairways and clusters were located by palaeogeomorphologic analysis. The border of a single reef was determined on the seismic attribute of instantaneous phase. Inter-reef connectivity was determined by spectral imaging. The technique of 3D visualization was used to delineate the border of a reef fairway or reef cluster and single-reef distribution. Finally, 4 reef fairways and 1 zone with superposed reefs were identified in the Changxing Fm in the Yuanba Gasfield; 21 reef clusters and 90 single reefs were interpreted. The cap of single reefs ranges from 0.12 to 3.62 km2, with an average of 0.99 km2. 3.2.2. Quantitative thin reef reservoir prediction Reef models were used to guide reservoir prediction. Based on reef identification, sedimentary microfacies controlled impedance inversion, GR pseudo-acoustic inversion, prestack geostatistical inversion, and 3D visualization were jointly used to quantitatively predict thin reservoir beds inside reefs. Sedimentary microfacies controlled impedance inversion aimed at predicting total reservoir thickness. Mud effect was eliminated by GR pseudo-acoustic inversion. Reservoir
Fig. 4. Reservoir correlation section from Wells YB12 to YB101.
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Fig. 5. Schematic Changxing Fm gas reservoir section from Well YB10-1H to Well YB9.
thickness for different microfacies was estimated by prestack geostatistical inversion. The technique of 3D visualization was employed to reveal reservoir distribution inside organic reefs. Finally, favorable biohermal reservoir beds were predicted to be 155.19 km2. The average thickness of high-graded (Grade I þ II) reservoir beds is 25, 30, 40, 35 and 20 m, respectively, in No. 1, No. 2, No. 3 and No. 4 reef fairways and the zone with superposed organic reefs and banks (Fig. 8). 3.2.3. Gas detection Gas accumulations were predicted by a joint utilization of poststack absorptive attenuation, prestack elastic impedance, Poisson's ratio reflectivity, Lame's coefficients and data structure. Well drilling results are reconciled with the prediction.
No. 1 reef fairway contains water as a whole and has nonuniform gasewater contacts. Formation water occurs locally in No. 2 reef fairway and only at the structural lows in No. 3 and No. 4 reef fairways. 3.3. Optimized horizontal well design for belt-like small biohermal gas reservoirs 3.3.1. Well type optimization In view of low yield and less controlled reserves of vertical wells, development well types were determined in accordance with the Changxing Fm reef distribution, organic reef and reservoir models, and results of small reef prediction and gas detection. Economic production rate limit and well controlled
Fig. 6. Dolomitization models for different reef-facies reservoirs (at the crest and back reef).
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Fig. 7. Single-reef and reef-cluster development and reservoir distribution models for the Changxing Fm, Yuanba Gasfield.
reserves were also taken into account. (1) Organic reefs with a number of scattered or thick reservoir beds in vertical direction would be drilled via a high angle hole. (2) Organic reefs with concentrated reservoir beds, which have a number of reef caps
in lateral direction or water layers at the bottom, would be drilled via a horizontal well. In the Yuanba Gasfield, the Changxing Fm gas reservoir would be recovered mainly via horizontal wells and subsequently via high angle holes.
Fig. 8. Grade I þ II reservoir thickness prediction map for the Changxing Fm, Yuanba Gasfield.
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3.3.2. Optimized horizontal well design In terms of reef clusters with small single reef and poor inter-reef connectivity, gas accumulations would be recovered via horizontal wells to improve recovery efficiency. For a number of multi-phase reefs (clusters) growing in vertical direction, horizontal wells and high angle holes would be combined to improve their vertical recovery efficiency. Gas reservoirs in the reefs (clusters) with local bottom water would be recovered via horizontal wells to avoid water layers and bottom water coning, so as to extend the water-free production period (Fig. 9). According to the inter-reef connectivity and recovery efficiency, horizontal well spacing was optimized to be 2000e3000 m and the horizontal interval to be 800 m for the reefs with good connectivity and large reserves. The reefs with the reserves possibly controlled by at most 2 wells were deployed with one well. A reef cluster with single-reef reserves less than economic reserves limit was deployed with one well. The horizontal wellbore track was designed to run parallel with the trend of the reef fairway, so that single reefs and high-graded reef-facies reservoir beds are penetrated as many as possible. The horizontal wellbore track was designed to run parallel with the trend of the reef fairway to ensure that more single reefs and high-graded reservoirs may be penetrated. For waterfree reefs, the target point A was designed to be located in the middle and upper parts of the good reservoirs and point B to be located in the middle and lower parts. For the reefs containing water, the horizontal interval should be located in the middle and upper parts of the reservoirs as much as possible to avoid water layers.
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3.4. Real-time horizontal wellbore track adjustment for ultra-deep thin reservoirs It is hard to guide a long horizontal wellbore track along the pre-designed route to penetrate a number of high-graded heterogeneous thin reservoirs in the ultra-deep zone with large tectonic relief. To address the issue of lithologic identification and reservoir evaluation which are difficult to achieve by conventional carbonate logging, X-ray fluorescence and nuclear magnetic resonance data were used to build a template for carbonate interpretation and to evaluate reservoir properties. Consequently, it is possible to realize rapid lithologic identification and reservoir evaluation while drilling. The horizontal wellbore track was adjusted to penetrate ultra-deep belt-like small biohermal gas reservoirs based on dolomite and high-graded reservoir interpretation, true cuttings depth control, and target point adjustment. Lithologies, petrophysical properties and gas content were interpreted and traced by special logging. The interpretation results were then used to guide the operation of increasing or decreasing hole-angle by slide steering drilling tools. 4. Application results 1) Quantitative prediction was guided by reef development and reservoir distribution models. Based on prediction results, fluid distribution and single-well productivity, 4 reef fairways, the zone with superposed organic reefs and banks, and a bank zone around Well Yuanba 12 were selected for development and production. The development plans were drafted separately for production test and progressive development of the Changxing Fm gas reservoir of 20 108 m3 in the Yuanba Gasfield. Among 37
Fig. 9. Schematic optimized well design for different types of biohermal reservoirs.
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2)
3)
4)
5)
wells designed for production, 12 wells were transferred from exploratory wells and 25 (horizontal) wells were deployed for development evaluation and development. There were 25 development wells (17 horizontal wells, 7 high angle holes and directional wells, and 1 vertical well). Drilling of all the development appraisal wells and development wells was finished with a success ratio being 100%; nearly 95% of reservoir beds predicted were drilled; over 82% of reservoir beds predicted were drilled via horizontal wells. Well drilling results were in agreement with reservoir prediction results, which demonstrated the credibility and accuracy of geologic studies, geophysical prediction and real-time wellbore track adjustment. All the horizontal wells and high-angle holes tested had high yields. The average open flow capacity (297 104 m3/d) was 1.9 times that (156 104 m3/d) of neighboring vertical wells. Combination gas productivity reached 40 108 m3/a. A large gas field was constructed; it is the first biohermal gas field with a high sulfur content buried at depth of 7000 m underground in China. Since the production of Yuanba Gasfield in December 2014, all the indicators were in agreement with the design. By the end of 2015, 22 wells had been put into production; proration production reached 880 104 m3/d. Combination gas, detergent gas and sulfur yields reached 17.69 108 m3, 16.41 108 m3, and 13.8 104 t, respectively, in 2015. Newly increased output value and profits reached CNY2.487 billion and CNY0.91 billion, respectively. The successful development of Yuanba Gasfield demonstrated the advanced techniques for gas field development with high sulfur content in China. In addition, the Yuanba Gasfield is another base for the Sichuan-to-East China Gas Transmission Pipeline project. Commercial gas production in the field guaranteed a consistent long-term gas supply to more than 70 cities in six provinces and two direct-controlled municipalities along the pipeline; this would be of great significance to the industrial restructuring in central and western China and the economic development in the regions along the Yangtze River.
References [1] Huang Liming. New progresses in safe, clean and efficient development technologies for high-sulfur gas reservoirs. Nat Gas Ind 2015;35(4):1e6. [2] Li Luguang. Progress in and developing orientation of technologies for the recovery and production of high-sulfur gas reservoirs in China. Nat Gas Ind 2013;33(1):18e24. [3] Du Zhimin. Oversea experiences of acid gas reservoir development and their enlightenments. Nat Gas Ind 2006;26(12):35e7. [4] Jia Ailin, Yan Haijun, Guo Jianlin, He Dongbo, Wei Tiejun. Characteristics and experiences of the development of various giant gas fields all over the world. Nat Gas Ind 2014;34(10):33e46. [5] Zhang Guangya, Ma Feng, Liang Yingbo, Zhao Zhe, Qin Yanqun, Liu Xiaobing. Domain and theoryetechnology progress of global deep oil & gas exploration. Acta Pet Sin 2015;36(9):1156e66. [6] Jia Chengzao, Pang Xiongqi. Research processes and main development directions of deep hydrocarbon geological theories. Acta Pet Sin 2015;36(12):1457e69.
[7] Dai Jinxing, Wu Wei, Fang Chenchen, Liu Dan. Exploration and development of large gas fields in China since 2000. Nat Gas Ind 2015;35(1):1e9. [8] Zhao Wenzhi, Hu Suyun, Liu Wei, Wang Tongshan, Li Yongxin. Petroleum geological features and exploration prospect in deep marine carbonate strata onshore China: a further discussion. Nat Gas Ind 2014;34(4):1e9. [9] Huang Fuxi, Yang Tao, Yan Weipeng, Guo Bincheng, Ma Hong. Comparison and analysis of reef-bank gas reservoirs in Longgang and Yuanba areas in Sichuan Basin. China Pet Explor 2014;19(3):12e20. [10] Ma Yongsheng, Cai Xunyu, Zhao Peirong. The research status and advances in porosity evolution and diagenesis of deep carbonate reservoir. Earth Sci Front 2011;18(4):181e92. [11] Ma Yongsheng, Mou Chuanlong, Tan Qinyin, Yu Qian. A discussion on KaijiangeLiangping ocean trough. Oil Gas Geol 2006;27(3):326e31. [12] Xu Anna, Wang Zecheng, Jiang Xingfu, Zhai Xiufen, Yin Jifeng. Morphological characteristics of platform margins along the KaijiangeLiangping Trough and their influences on reservoir development in the Sichuan Basin. Nat Gas Ind 2014;34(4):37e43. [13] Zhang Bing, Zheng Rongcai, Wen Huaguo, Hu Zhonggui, Luo Aijun, Wen Qibing. Identification criteria and prediction of reef and shoal facies reservoirs of the Changxing formation in the eastern KaijiangeLiangping area intraplatform trough. Geol J China Univ 2009;15(2):273e84. [14] Fan Xiaojun. Control sedimentation characteristics of upper permian Changxing formation in Yuanba area and its control action for reservoir. J Southwest Pet Univ Sci Technol Ed 2015;37(2):39e48. [15] Deng Jian, Duan Jinbao, Wang Zhenghe, Wang Mingfa. Research on the reef characteristic of Changxing formation in Yuanba area of northeast Sichuan province. J Southwest Pet Univ Sci Technol Ed 2014;36(4):63e72. [16] Ma Yongsheng, Cai Xunyu, Zhao Peirong. Characteristics and formation mechanisms of reef-shoal carbonate reservoirs of ChangxingeFeixianguan formations, Yuanba Gasfield. Acta Pet Sin 2014;35(6):1001e11. [17] Wang Guoru, Guo Tonglou, Fu Xiaoyue. Characteristics and spatialetemporal configuration of platform margin reef-bank system, Changxing formation in Yuanba area, northeastern Sichuan Basin. Pet Geol Recovery Effic 2011;18(4):40e3. [18] Flood PG. Geological history of the reef. In: Mather P, Bennett I, editors. A coral reef handbook. Sydney: Surrey Beatty & Sons; 1993. p. 3e6. [19] Guo Tonglou. Sequence strata of the platform edge in the Changxing and Feixianguan formations in the Yuanba area, northeastern Sichuan Basin and their control on reservoirs. Acta Pet Sin 2011;32(3):387e94. [20] Zhao Wenguang, Guo Tonglou, Cai Zhongxian, Huang Renchun, Yang Bo, Duan Jinbao. The controlling factors and types of carbonate reef of permian Changxing formation in northeast of Sichuan Basin. Geoscience 2010;24(5):951e6. [21] Liu Shu, Tang Jianming, Ma Yongsheng, Zhao Shuang. Prediction of reef and shoal facies reservoirs in ChangxingeFeixianguan formations in northeastern Sichuan Basin. Oil Gas Geol 2006;27(3):332e47. [22] Zhou Gang, Zheng Rongcai, Wang Jiong, Li Yu, Wen Qibing, Xu Fabo. Reef and shoal facies reservoir prediction of Changxing formation in eastern Sichuan and northern Chongqing. Lithol Reserv 2009;21(1):15e21. [23] Chen Zongqing. Changxing formation biohermal gas pools and natural gas exploration, Sichuan Basin. Pet Explor Dev 2008;35(2):148e63. [24] Wang Yigang, Wen Yingchu, Zhang Fan, Yang Yu, Zhang Jing. Distribution law of the organic reefs in Changxing formation of upper permian in east Sichuan. Nat Gas Ind 1998;18(6):10e5. [25] Zhao Bangliu, Du Xiaodi. Geological features of bioherms and corresponding geophysical recognization system. Beijing: Petroleum Industry Press; 2009. p. 29e30. [26] Ma Yongsheng, Mou Chuanlong, Guo Xusheng, Tan Qinyin, Yu Qian. Characteristic and framework of the Changxingian sedimentation in the northeastern Sichuan Basin. Geol Rev 2006;52(1):25e31. [27] Li Hongtao, Long Shengxiang, You Yuchun, Liu Guoping, Li Xiupeng. Sequence and sedimentary characteristics of Changxing Formation organic reefs in the Yuanba Gasfield and their controlling effects on reservoir development in the Sichuan Basin. Nat Gas Ind 2015;35(10):1e10. [28] Wang Yigang, Zhang Jing, Yang Yu, Liu Huayi, Yu Xiaofeng. A formation mechanism of upper permian Changxing reef gas reservoirs in the eastern part of Sichuan Basin. Mar Orig Pet Geol 2000;5(2):145e52.
ScienceDirect Natural Gas Industry B 3 (2016) 537e544 www.elsevier.com/locate/ngib
Research Article
Characteristics of the Changxing Fm biohermal gas reservoir in the Yuanba Gasfield, Sichuan Basin and development countermeasures* Wu Hengzhi a, Li Zhongping a, Ke Guangming b,* b
a Sinopec Southwest Branch Company, Chengdu, Sichuan 610081, China Exploration and Development Research Institute, Sinopec Southwest Branch Company, Chengdu, Sichuan 610081, China
Received 8 July 2016; accepted 25 September 2016 Available online 23 June 2017
Abstract Located in the Sichuan Basin, the Yuanba Gasfield is the deepest high-sulfur carbonate gas field among those discovered in the world. Its biohermal gas reservoir of the Upper Permian Changxing Fm is characterized by ultra depth, multi-stage small and scattered reef, thin reservoir, poor physical properties, strong heterogeneity, complex fluid distribution, and low production of vertical wells. The development of the biohermal gas reservoir is subject to many difficulties. For example, it is necessary to deepen the studies on timeespace distribution laws of reef dolomite reservoirs; it is difficult to characterize small reefs precisely and predict thin reservoirs quantitatively; the deployment and optimization design of horizontal wells are influenced by multiple factors; and the difficulty for horizontal wells with long horizontal sections to run through high-quality thin reservoirs is high. In order to develop the Yuanba Gasfield efficiently, therefore, it is necessary to carry out a series of technical researches on the distribution laws and development models of biohermal reservoirs, precise characterization of small reefs, quantitative prediction of thin reservoirs, optimization design of horizontal wells in banded small reef gas reservoirs, and real-time trajectory optimization and adjustment of horizontal wells in ultra-deep thin reservoirs. These research results provide a powerful support for the development and construction of the Yuanba Gasfield. Based on these technologies, China's first ultra-deep high-sulfur large biohermal gas field was built with a mixed gas annual production capacity of 40 108 m3. The successful commissioning of the Yuanba Gasfield lays a basis for the leading position of China in the field of high-sulfur gas field development. In addition, it is of great significance to the long-term stable gas supply in 70 cities of six provinces and two municipalities along the “Sichuan-to-East China Gas Transmission Pipeline”, as well as to the industrial structure adjustment in centralewestern China and the economic development along the Yangtze River. © 2017 Sichuan Petroleum Administration. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Keywords: Sichuan Basin; Yuanba Gasfield; Late permian; Biohermal gas reservoir; Reservoir; Development model; Reef characterization; Horizontal well design; Trajectory optimization
The Yuanba Gasfield is the deepest carbonate gas field with high sulfur content ever discovered around the world. Gas accumulations in the Upper Permian Changxing Fm mainly occur in marginal platform dolomite of organic reef and bank facies. More and more gas reservoirs with high sulfur content * Project supported by the National Science and Technology Major Project in the 13th Five-Year Plan “High-efficiency development of ultra-deep bioherm gas reservoirs with bottom water” (No.: 2016ZX05017-005). * Corresponding author. E-mail address: [email protected] (Ke GM.). Peer review under responsibility of Sichuan Petroleum Administration.
have been discovered in China and abroad [1e3]. The development of such reservoirs is among the major national energy strategies for promoting gas industry and technical research in China. But commercial production is challenging and there are no successful cases for Ref. [4]. In this paper, reservoir distribution, quantitative prediction of small reefs and thin reservoirs, horizontal well design for belt-like small biohermal gas reservoirs, and real-time adjustment of horizontal wellbore track through ultra-deep thin reservoirs are discussed, followed by the analyses of possible strategies on high-efficiency gas reservoir development.
http://dx.doi.org/10.1016/j.ngib.2017.05.003 2352-8540/© 2017 Sichuan Petroleum Administration. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
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1. Gas reservoir geological features The Changxing Fm biohermal gas reservoir in the Yuanba Gasfield features large burial depth, small size, scattered distribution, small thickness, poor petrophysical properties, strong heterogeneity, complex fluid distribution, and low vertical-well production.
and 0.250 mD and above 1 mD (Fig. 1). The wide span of permeability indicates strong heterogeneity. As per log interpretation of 23 wells, the porosity of Changxing Fm reeffacies reservoirs ranges from 2.0% to 14.2% (Fig. 2), with an average of 4.8%. The permeability ranges from 0.01 to 13483.89 mD, with a geometric average of 0.99 mD. In general, the Changxing Fm reservoir is of low porosity and medium to low permeability.
1.1. Ultra-deep reservoirs Tectonically, the Yuanba Gasfield lies at the joint of the northern Sichuan depression and central Sichuan gentle structural belt in the Sichuan Basin. The Changxing Fm presents a NE-inclined monoclinal structure. Its average burial depth exceeds 6600 m (the top and bottom of the Changxing Fm were drilled at 6239e7244 m). Among deep reservoirs in China for exploration and development in recent years [5e10], the Changxing Fm gas reservoir in the Yuanba field is the deepest one for commercial production. The Changxing Fm gas reservoir is 700e1500 m deeper than the Longgang gas field, 800e1500 m deeper than the Puguang field, 2600 m deeper than the Wubaiti field, and 3200e3700 m deeper than the Tieshan field. 1.2. Multi-phase small scattered reefs As per well drilling and seismic data, the Yuanba Gasfield was on the marginal gentle-slope platform on the west side of the KaijiangeLiangping shelf during the Changxing Fm deposition [11e13]. The degree of slope was 8 e10 [14e17]. In such an environment with relatively weak hydrodynamic conditions, organic reefs grew slowly in the form of vertical accretion and lateral migration. As a result, many late reefs are superimposed upon early reefs and scatter laterally in a wide area; a single reef is small in size. Flood [18]made a study of bioherm limestone deposited in the Heron Island in 1993. They found that reef-bank deposits on the marginal gentleslope platform nowadays have similar features, i.e. small single reef size, multi-phase stacking of reefs in vertical direction, and scattered distribution in lateral direction. As per the studies made by Ma et al. [16], Wang et al. [17], Guo [19], and Zhao et al. [20]. On the temporalespatial configuration of the Changxing Fm marginal platform reef-bank system, multiphase organic reefs exist in the Yuanba Gasfield and migrate laterally in different directions. 1.3. Strong heterogeneity 1.3.1. Poor reservoir properties Analysis of 465 core samples acquired from 16 wells shows that the porosity of the Changxing Fm reef-facies reservoirs in the Yuanba Gasfield ranges from 0.53% to 23.59%, with an average of 4.87%. Samples with a porosity above 2% average at 5.76%. About 47% of the total samples have a porosity of 2e5%. About 21% of the total samples have a porosity below 2% and between 5% and 10%. The permeability ranges from 0.0007 to 1720.7190 mD, with a geometric average of 0.5111 mD. Most samples have a permeability between 0.002
1.3.2. Small reservoir thickness. In the Yuanba Gasfield, the average thickness of reef-facies reservoirs in 23 wells is 58.8 m. Grade I gas layers are 0e15.8 m thick with an average of 2.66 m and account for 4.72% of the total reservoir thickness. Grade II gas layers are 0e56.3 m thick with an average of 18.5 m and account for 32.85% of the total reservoir thickness. Grade III gas layers are 2.1e67.3 m thick with an average of 25.8 m and account for 45.83% of the total reservoir thickness. Gas-bearing layers are 0e20.8 m thick with an average of 2.21% and account for 3.92% of the total reservoir thickness. Gasewater layers are 0e34.65 m thick with an average of 2.72 m and account for 4.82% of the total reservoir thickness. Water layers with low gas saturation are 0e59.6 m with an average of 4.05 m and account for 7.19% of the total reservoir thickness. Water layers are 0e8.45 m thick with an average of 0.37 m and account for 0.65% of the total reservoir thickness (Fig. 3). 1.3.3. Strong heterogeneity As per reservoir correlation, the Changxing Fm reservoir of reef and bank facies exhibits strong heterogeneity both in vertical and lateral directions. Generally speaking, different types of reservoirs have different thickness and may not be connected laterally; reservoir thickness also changes greatly in lateral direction (Fig. 4). 1.4. Complex gasewater distribution As per log interpretation and testing results, it is inferred that the Changxing Fm gas reservoir in the Yuanba Gasfield exists in a separate reef and has relatively isolated gasewater system. There are no regional water bodies which occur as edge water or bottom water. Studies show that gasewater distribution in reservoirs of reef facies in No. 2, No. 3 and No. 4 reef fairways is obviously dominated by present structures. Generally, the wells drilled at the structural lows produced water, especially in YB273, YB28 and YB103H wells. But in No. 1 reef fairway, there is no remarkable relationship between gasewater production and structural location. Wells YB9, YB107 and YB10-1H all produced water with different volumes (Fig. 5). 1.5. Low vertical-well productivity As per the testing results of 15 wells, vertical wells drilled in the Yuanba Gasfield have low productivity of Changxing Fm biohermal gas. Openflow capacity was tested to range at (7e318) 104 m3/d and the average was 149 104 m3/d.
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Fig. 1. Porosity and permeability histograms based on core data of Changxing Fm reef-facies reservoir in the Yuanba Gasfield.
2. Challenges to commercial gas production In view of complex gas reservoir geological features, it is hard to delineate biohermal reservoir distribution, predict small reefs and thin reservoirs, deploy and optimize development wells, and adjust wellbore track in real time. The challenges are detailed as follows. (1) The Changxing Fm organic reefs formed in multi-period in the Yuanba Gasfield are small in size and scatter throughout the marginal gentleslope platform. Besides, reservoir rocks are highly heterogeneous. Thus it is necessary to deepen the understanding of temporalespatial reservoir distribution. (2) Due to ultragreat burial depth of the intervals being investigated, seismic signals are of weak energy and low signal-to-noise ratio and resolution [21,22], which makes it difficult to quantitatively predict small reefs and thin reservoirs. (3) It is hard to realize profitable production via vertical wells. The deployment and optimization of horizontal wells in small reefs and thin reservoirs are dependent on many factors. (4) It is hard to laterally penetrate a high-graded thin reservoir bed of 1000 m buried at nearly 7000 m through horizontal well drilling. 3. Development countermeasures 3.1. Biohermal reservoir distribution law and dolomitization models 3.1.1. Major controlling factors for reef-facies dolomite reservoirs Studies [23,24] show that the formation of organic reefs is greatly dependent on ancient land forms at the depositional
stage. In the Yuanba Gasfield, organic reefs are most likely to occur at the structural highs of the marginal platform, slope break belt, and intra-platform highland [25]. The Changxing Fm reservoir rocks with good properties in the Yuanba Gasfield are mainly organic reefs on the marginal platform. Lateral reservoir distribution is related to sedimentary microfacies. Vertical reservoir distribution is dominated by high-frequency cycles at the depositional stage. Reservoir rocks concentrate in the middle and upper parts of the descending hemicycle in the fourth order sequence; this is because early native rocks tended to be dolomitized due to sea level drop during deposition in the descending hemicycle in the fourth order sequence [26e28]. For organic reefs on the marginal platform, reservoir variations in lateral and vertical directions are related to differential diageneses, which gave rise to a strong heterogeneity of reef-facies dolomite reservoirs. The evolution of dolomite reservoirs in the Yuanba Gasfield is dependent on dolomitization and chemical erosion. Contemporaneous high-salinity dolomitization and medium-term shallow-burial dolomitization gave birth to dolomite, which was corroded by organic acids and sulfates at the middle and late stages to form pore space for the Changxing Fm gas accumulation. A single organic reef is vertically subdivided into reef base, reef core and reef cap and laterally subdivided into reef front, reef crest and back reef. The reef crest (reef cap) experienced early evaporative pumping dolomitization, shallow-burial dolomitization, and intense middle and late chemical erosion and thus has the best reservoir rocks. The back reef experienced early reflux permeation dolomitization, shallow-burial dolomitization, and intense middle and late chemical erosion and also has good reservoir rocks (Fig. 6).
Fig. 2. Average porosity histograms based on log interpretation of Changxing Fm reef-facies reservoirs in the Yuanba Gasfield.
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Fig. 3. Thickness histograms based on log interpretation of Changxing Fm reef-facies reservoir in the Yuanba Gasfield.
3.1.2. Reef-facies reservoir distribution law The Changxing Fm organic reefs in the Yuanba Gasfield may form in a single phase or two phases (Fig. 7). Vertically, a single-phase reef reservoir mainly occurs at the cap (with an average thickness of 39.9 m); two-phase reservoirs mainly occur at the upper phase-II cap (with an average thickness of 42.9 m) and some occur at the lower phase-I cap (with an average thickness of 21.6 m). Laterally, reef reservoirs mainly distribute at the crest (the average thickness is 77.0 m; the average thickness of Grade I þ II layers is 37.0 m) and some distribute at the back reef (the average thickness is 38.3 m; the average thickness of Grade I þ II layers is 11.0 m). Some thin reservoirs exist at the reef front (the average thickness is 32.6 m; the average thickness of Grade I þ II layers is 9.5 m). 3.1.3. Reef cluster development and reservoir distribution models The Changxing Fm organic reefs in the Yuanba Gasfield were deposited on the marginal gentle-slope platform. Due to ancient land forms at the depositional stage and frequent sea level changes, organic reefs formed in multi-period feature small size and scattered distribution. Complex occurrences of organic reefs and reef-facies reservoirs make it difficult to optimize the deployment of development wells and wellbore track. After comprehensive analyses of bioherm stratigraphic features and seismic reflection configurations, reef clusters and reef-facies reservoirs with 5 models were described, i.e. vertical progradation (A), vertical retrogradation (B), lateral juxtaposition (C), lateral migration (D), and superposition (E)
(Fig. 7). These models would be used in reef identification, quantitative reservoir prediction, development well deployment, and wellbore track optimization. 3.2. Fine reef description and quantitative reservoir prediction 3.2.1. Ultra-deep small reef identification and description Reef models were used to guide reef identification. Reef fairways and clusters were located by palaeogeomorphologic analysis. The border of a single reef was determined on the seismic attribute of instantaneous phase. Inter-reef connectivity was determined by spectral imaging. The technique of 3D visualization was used to delineate the border of a reef fairway or reef cluster and single-reef distribution. Finally, 4 reef fairways and 1 zone with superposed reefs were identified in the Changxing Fm in the Yuanba Gasfield; 21 reef clusters and 90 single reefs were interpreted. The cap of single reefs ranges from 0.12 to 3.62 km2, with an average of 0.99 km2. 3.2.2. Quantitative thin reef reservoir prediction Reef models were used to guide reservoir prediction. Based on reef identification, sedimentary microfacies controlled impedance inversion, GR pseudo-acoustic inversion, prestack geostatistical inversion, and 3D visualization were jointly used to quantitatively predict thin reservoir beds inside reefs. Sedimentary microfacies controlled impedance inversion aimed at predicting total reservoir thickness. Mud effect was eliminated by GR pseudo-acoustic inversion. Reservoir
Fig. 4. Reservoir correlation section from Wells YB12 to YB101.
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Fig. 5. Schematic Changxing Fm gas reservoir section from Well YB10-1H to Well YB9.
thickness for different microfacies was estimated by prestack geostatistical inversion. The technique of 3D visualization was employed to reveal reservoir distribution inside organic reefs. Finally, favorable biohermal reservoir beds were predicted to be 155.19 km2. The average thickness of high-graded (Grade I þ II) reservoir beds is 25, 30, 40, 35 and 20 m, respectively, in No. 1, No. 2, No. 3 and No. 4 reef fairways and the zone with superposed organic reefs and banks (Fig. 8). 3.2.3. Gas detection Gas accumulations were predicted by a joint utilization of poststack absorptive attenuation, prestack elastic impedance, Poisson's ratio reflectivity, Lame's coefficients and data structure. Well drilling results are reconciled with the prediction.
No. 1 reef fairway contains water as a whole and has nonuniform gasewater contacts. Formation water occurs locally in No. 2 reef fairway and only at the structural lows in No. 3 and No. 4 reef fairways. 3.3. Optimized horizontal well design for belt-like small biohermal gas reservoirs 3.3.1. Well type optimization In view of low yield and less controlled reserves of vertical wells, development well types were determined in accordance with the Changxing Fm reef distribution, organic reef and reservoir models, and results of small reef prediction and gas detection. Economic production rate limit and well controlled
Fig. 6. Dolomitization models for different reef-facies reservoirs (at the crest and back reef).
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Fig. 7. Single-reef and reef-cluster development and reservoir distribution models for the Changxing Fm, Yuanba Gasfield.
reserves were also taken into account. (1) Organic reefs with a number of scattered or thick reservoir beds in vertical direction would be drilled via a high angle hole. (2) Organic reefs with concentrated reservoir beds, which have a number of reef caps
in lateral direction or water layers at the bottom, would be drilled via a horizontal well. In the Yuanba Gasfield, the Changxing Fm gas reservoir would be recovered mainly via horizontal wells and subsequently via high angle holes.
Fig. 8. Grade I þ II reservoir thickness prediction map for the Changxing Fm, Yuanba Gasfield.
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3.3.2. Optimized horizontal well design In terms of reef clusters with small single reef and poor inter-reef connectivity, gas accumulations would be recovered via horizontal wells to improve recovery efficiency. For a number of multi-phase reefs (clusters) growing in vertical direction, horizontal wells and high angle holes would be combined to improve their vertical recovery efficiency. Gas reservoirs in the reefs (clusters) with local bottom water would be recovered via horizontal wells to avoid water layers and bottom water coning, so as to extend the water-free production period (Fig. 9). According to the inter-reef connectivity and recovery efficiency, horizontal well spacing was optimized to be 2000e3000 m and the horizontal interval to be 800 m for the reefs with good connectivity and large reserves. The reefs with the reserves possibly controlled by at most 2 wells were deployed with one well. A reef cluster with single-reef reserves less than economic reserves limit was deployed with one well. The horizontal wellbore track was designed to run parallel with the trend of the reef fairway, so that single reefs and high-graded reef-facies reservoir beds are penetrated as many as possible. The horizontal wellbore track was designed to run parallel with the trend of the reef fairway to ensure that more single reefs and high-graded reservoirs may be penetrated. For waterfree reefs, the target point A was designed to be located in the middle and upper parts of the good reservoirs and point B to be located in the middle and lower parts. For the reefs containing water, the horizontal interval should be located in the middle and upper parts of the reservoirs as much as possible to avoid water layers.
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3.4. Real-time horizontal wellbore track adjustment for ultra-deep thin reservoirs It is hard to guide a long horizontal wellbore track along the pre-designed route to penetrate a number of high-graded heterogeneous thin reservoirs in the ultra-deep zone with large tectonic relief. To address the issue of lithologic identification and reservoir evaluation which are difficult to achieve by conventional carbonate logging, X-ray fluorescence and nuclear magnetic resonance data were used to build a template for carbonate interpretation and to evaluate reservoir properties. Consequently, it is possible to realize rapid lithologic identification and reservoir evaluation while drilling. The horizontal wellbore track was adjusted to penetrate ultra-deep belt-like small biohermal gas reservoirs based on dolomite and high-graded reservoir interpretation, true cuttings depth control, and target point adjustment. Lithologies, petrophysical properties and gas content were interpreted and traced by special logging. The interpretation results were then used to guide the operation of increasing or decreasing hole-angle by slide steering drilling tools. 4. Application results 1) Quantitative prediction was guided by reef development and reservoir distribution models. Based on prediction results, fluid distribution and single-well productivity, 4 reef fairways, the zone with superposed organic reefs and banks, and a bank zone around Well Yuanba 12 were selected for development and production. The development plans were drafted separately for production test and progressive development of the Changxing Fm gas reservoir of 20 108 m3 in the Yuanba Gasfield. Among 37
Fig. 9. Schematic optimized well design for different types of biohermal reservoirs.
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2)
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wells designed for production, 12 wells were transferred from exploratory wells and 25 (horizontal) wells were deployed for development evaluation and development. There were 25 development wells (17 horizontal wells, 7 high angle holes and directional wells, and 1 vertical well). Drilling of all the development appraisal wells and development wells was finished with a success ratio being 100%; nearly 95% of reservoir beds predicted were drilled; over 82% of reservoir beds predicted were drilled via horizontal wells. Well drilling results were in agreement with reservoir prediction results, which demonstrated the credibility and accuracy of geologic studies, geophysical prediction and real-time wellbore track adjustment. All the horizontal wells and high-angle holes tested had high yields. The average open flow capacity (297 104 m3/d) was 1.9 times that (156 104 m3/d) of neighboring vertical wells. Combination gas productivity reached 40 108 m3/a. A large gas field was constructed; it is the first biohermal gas field with a high sulfur content buried at depth of 7000 m underground in China. Since the production of Yuanba Gasfield in December 2014, all the indicators were in agreement with the design. By the end of 2015, 22 wells had been put into production; proration production reached 880 104 m3/d. Combination gas, detergent gas and sulfur yields reached 17.69 108 m3, 16.41 108 m3, and 13.8 104 t, respectively, in 2015. Newly increased output value and profits reached CNY2.487 billion and CNY0.91 billion, respectively. The successful development of Yuanba Gasfield demonstrated the advanced techniques for gas field development with high sulfur content in China. In addition, the Yuanba Gasfield is another base for the Sichuan-to-East China Gas Transmission Pipeline project. Commercial gas production in the field guaranteed a consistent long-term gas supply to more than 70 cities in six provinces and two direct-controlled municipalities along the pipeline; this would be of great significance to the industrial restructuring in central and western China and the economic development in the regions along the Yangtze River.
References [1] Huang Liming. New progresses in safe, clean and efficient development technologies for high-sulfur gas reservoirs. Nat Gas Ind 2015;35(4):1e6. [2] Li Luguang. Progress in and developing orientation of technologies for the recovery and production of high-sulfur gas reservoirs in China. Nat Gas Ind 2013;33(1):18e24. [3] Du Zhimin. Oversea experiences of acid gas reservoir development and their enlightenments. Nat Gas Ind 2006;26(12):35e7. [4] Jia Ailin, Yan Haijun, Guo Jianlin, He Dongbo, Wei Tiejun. Characteristics and experiences of the development of various giant gas fields all over the world. Nat Gas Ind 2014;34(10):33e46. [5] Zhang Guangya, Ma Feng, Liang Yingbo, Zhao Zhe, Qin Yanqun, Liu Xiaobing. Domain and theoryetechnology progress of global deep oil & gas exploration. Acta Pet Sin 2015;36(9):1156e66. [6] Jia Chengzao, Pang Xiongqi. Research processes and main development directions of deep hydrocarbon geological theories. Acta Pet Sin 2015;36(12):1457e69.
[7] Dai Jinxing, Wu Wei, Fang Chenchen, Liu Dan. Exploration and development of large gas fields in China since 2000. Nat Gas Ind 2015;35(1):1e9. [8] Zhao Wenzhi, Hu Suyun, Liu Wei, Wang Tongshan, Li Yongxin. Petroleum geological features and exploration prospect in deep marine carbonate strata onshore China: a further discussion. Nat Gas Ind 2014;34(4):1e9. [9] Huang Fuxi, Yang Tao, Yan Weipeng, Guo Bincheng, Ma Hong. Comparison and analysis of reef-bank gas reservoirs in Longgang and Yuanba areas in Sichuan Basin. China Pet Explor 2014;19(3):12e20. [10] Ma Yongsheng, Cai Xunyu, Zhao Peirong. The research status and advances in porosity evolution and diagenesis of deep carbonate reservoir. Earth Sci Front 2011;18(4):181e92. [11] Ma Yongsheng, Mou Chuanlong, Tan Qinyin, Yu Qian. A discussion on KaijiangeLiangping ocean trough. Oil Gas Geol 2006;27(3):326e31. [12] Xu Anna, Wang Zecheng, Jiang Xingfu, Zhai Xiufen, Yin Jifeng. Morphological characteristics of platform margins along the KaijiangeLiangping Trough and their influences on reservoir development in the Sichuan Basin. Nat Gas Ind 2014;34(4):37e43. [13] Zhang Bing, Zheng Rongcai, Wen Huaguo, Hu Zhonggui, Luo Aijun, Wen Qibing. Identification criteria and prediction of reef and shoal facies reservoirs of the Changxing formation in the eastern KaijiangeLiangping area intraplatform trough. Geol J China Univ 2009;15(2):273e84. [14] Fan Xiaojun. Control sedimentation characteristics of upper permian Changxing formation in Yuanba area and its control action for reservoir. J Southwest Pet Univ Sci Technol Ed 2015;37(2):39e48. [15] Deng Jian, Duan Jinbao, Wang Zhenghe, Wang Mingfa. Research on the reef characteristic of Changxing formation in Yuanba area of northeast Sichuan province. J Southwest Pet Univ Sci Technol Ed 2014;36(4):63e72. [16] Ma Yongsheng, Cai Xunyu, Zhao Peirong. Characteristics and formation mechanisms of reef-shoal carbonate reservoirs of ChangxingeFeixianguan formations, Yuanba Gasfield. Acta Pet Sin 2014;35(6):1001e11. [17] Wang Guoru, Guo Tonglou, Fu Xiaoyue. Characteristics and spatialetemporal configuration of platform margin reef-bank system, Changxing formation in Yuanba area, northeastern Sichuan Basin. Pet Geol Recovery Effic 2011;18(4):40e3. [18] Flood PG. Geological history of the reef. In: Mather P, Bennett I, editors. A coral reef handbook. Sydney: Surrey Beatty & Sons; 1993. p. 3e6. [19] Guo Tonglou. Sequence strata of the platform edge in the Changxing and Feixianguan formations in the Yuanba area, northeastern Sichuan Basin and their control on reservoirs. Acta Pet Sin 2011;32(3):387e94. [20] Zhao Wenguang, Guo Tonglou, Cai Zhongxian, Huang Renchun, Yang Bo, Duan Jinbao. The controlling factors and types of carbonate reef of permian Changxing formation in northeast of Sichuan Basin. Geoscience 2010;24(5):951e6. [21] Liu Shu, Tang Jianming, Ma Yongsheng, Zhao Shuang. Prediction of reef and shoal facies reservoirs in ChangxingeFeixianguan formations in northeastern Sichuan Basin. Oil Gas Geol 2006;27(3):332e47. [22] Zhou Gang, Zheng Rongcai, Wang Jiong, Li Yu, Wen Qibing, Xu Fabo. Reef and shoal facies reservoir prediction of Changxing formation in eastern Sichuan and northern Chongqing. Lithol Reserv 2009;21(1):15e21. [23] Chen Zongqing. Changxing formation biohermal gas pools and natural gas exploration, Sichuan Basin. Pet Explor Dev 2008;35(2):148e63. [24] Wang Yigang, Wen Yingchu, Zhang Fan, Yang Yu, Zhang Jing. Distribution law of the organic reefs in Changxing formation of upper permian in east Sichuan. Nat Gas Ind 1998;18(6):10e5. [25] Zhao Bangliu, Du Xiaodi. Geological features of bioherms and corresponding geophysical recognization system. Beijing: Petroleum Industry Press; 2009. p. 29e30. [26] Ma Yongsheng, Mou Chuanlong, Guo Xusheng, Tan Qinyin, Yu Qian. Characteristic and framework of the Changxingian sedimentation in the northeastern Sichuan Basin. Geol Rev 2006;52(1):25e31. [27] Li Hongtao, Long Shengxiang, You Yuchun, Liu Guoping, Li Xiupeng. Sequence and sedimentary characteristics of Changxing Formation organic reefs in the Yuanba Gasfield and their controlling effects on reservoir development in the Sichuan Basin. Nat Gas Ind 2015;35(10):1e10. [28] Wang Yigang, Zhang Jing, Yang Yu, Liu Huayi, Yu Xiaofeng. A formation mechanism of upper permian Changxing reef gas reservoirs in the eastern part of Sichuan Basin. Mar Orig Pet Geol 2000;5(2):145e52.