Chapter 11 Relief Well Engineering to Control Blowouts

Studier in Abnormal Pressures. Developments in Petroleum Science, 38 edited by W.H. Fertl, R.E. Chapman and R.F. Hotz 0 1994 Elsevier Science B.V.All rights reserved

319

Chapter 11 RELIEF WELL ENGINEERING TO CONTROL BLOWOUTS ROBERT DESBRANDES

11.1. INTRODUCTION

When formation pore pressure is underestimated and significantly exceeds the hydrostatic pressure exerted by the wellbore fluid, formation fluids start flowing into the borehole resulting in a “kick”. Most of the time such a kick is not severe and the well can be controlled. If a large kick occurs and the wellsite personnel and equipment are not fully prepared for it, the well blows out and frequently catches fire. Shallow blowouts, which occur as results of small gas pockets, usually cease as soon as the formation pressure is depleted or the well bridges, usually after a relatively short period. Deep blowouts may last for years and produce an enormous quantity of fluid if no attempt is made to control them. The most efficient way to control a blowout is to drill one or several relief wells which will reach the “wild” or uncontrolled well, above or at the producing problem formation. Fluid will then be injected to kill it. Surveys of Gulf Coast blowouts over the last twenty years have been made by Podio et al. (1983a, b) and Hughes et al. (1987). This chapter provides a brief discussion of the following considerations: flowrate estimates, control techniques, trajectory planning, relief well directional surveying, and distance ranging techniques. Several examples of typical blowouts related to overpressure will be presented.

11.2. BLOWOUT FLOWRATE

A well out of control discharges large amounts of hydrocarbons, usually gas. Estimates of the flowrate and downhole pressure are necessary to plan the control operations because metering devices cannot be installed. Calculations are made by crossplotting the formation resistance and the flow-string resistance (Hawkins et al., 1981).

11.2.1. Formation resistance Unless the reservoir is well known, the calculation procedures are based on a simple radial flow geometry. The reservoir is assumed circular of constant thickness. The volume of gas computed for a steady-state flow is given in practical metric units by:

320

R. DESBRANDES

(11-1)

where Qs, = volume of gas produced at standard conditions (1 atm and 15°C) in m3/d; k = reservoir permeability in pm2; h = reservoir thickness in m; Pe = reservoir pressure at radius re in kPa; P, = wellbore pressure at radius r, in kPa; p = average viscosity in mPa s; T = reservoir temperature in K Z = average gas deviation factor; and re/rw = ratio of external drainage radius to wellbore radius. In customary units: (11-la) where Qsc = volume of gas produced at standard conditions (14.7 psi and 60°F) in scf/d; k = reservoir permeability in D; h = reservoir thickness in ft; f e = reservoir pressure at radius re in psia; P, = wellbore pressure at radius r, in psia; p = average viscosity in cP; T = reservoir temperature in OR;Z = average gas deviation factor; and re/rw = ratio of external drainage radius to wellbore radius. The calculation is made for various values of P, resulting in a curve of the gas flowrate versus P, as shown schematically in Fig. 11-1. Transient flowrate calculation can be made at different times assuming that the pressure perturbation radius increases according to the following formula in practical metric units (Lee, 1982):

::/

re = 0.584 -

(11-2)

where re = perturbation radius in m; TR = time in days; p = average gas viscosity in mPa s; k = permeability in pm2; c = gas compressibility in kPa-'; and 4 = M Pa

0

20

30

BOTTOM HOLE P R E S S U R E , 1000 P S l A

Fig. 1 1 - 1 . Typical formation and flow string resistance curves. The flowrate and bottomhole pressure are read at the intersection of the two curves (after Hawkins et al., 1980).

321

RELIEF WELL ENGINEERING TO CONTROL BLOWOUTS M Po I0

0

100

20

30 25

0

2

80

0

20

0

60

e

15% W

2

(D

0

40

IC

(L

3

9LL

20

5

3 4 5 BOTTOM HOLE P R E S S U R E , 1000 P S l A I

2

0

Fig. 11-2.m i c a 1 transient formation resistance curves. The formation resistance curves vary with time as the pressure perturbation progresses toward the edge of the reservoir (after Hawkins et al., 1980).

formation porosity in fraction. In customary units: I

(11-2a) where re = perturbation radius in ft; TR = time in days; p = average gas velocity in cP; k = permeability in D; c = gas compressibility in psi-'; and = formation porosity in fraction. By using re in eq. 11-1 the flowrate can be calculated at different times for various wellbore pressures, as shown in Fig. 11-2. When the perturbation has reached the edge of the reservoir, an average reservoir pressure based on a material balance calculation must be used to compute the flowrate for a given bottomhole well pressure.

11.2.2. Flow-string resktance For a flowing gas well, the bottomhole well pressure is given in S.I. units by:

where Pw = bottomhole pressure in Pa; P, = surface pressure in Pa; p = gas density in kg/m3; z = elevation above reference level in m; Pf = pressure loss due to friction in Pa; v = velocity of gas in m/s; and g = acceleration due to gravity in m/s2. In customary units: (11-3a)

322

R. DESBRANDES

where P, = bottomhole pressure in psia; P, = surface pressure in psia; p = gas density in lbs/ft3; z = elevation above reference level in ft; Pf = pressure loss due to friction in psia; v = velocity of gas in ft/s; and g = acceleration due to gravity in ft/s2. The first integral term in eq. 11-3 accounts for the change in pressure due to potential energy along the flow path. The second is the change in pressure over the flow path due to friction. The third accounts for the change in pressure due to change in kinetic energy along the flow path. With the use of modern computers numerical integration of the basic terms in the general eq. 11-3 can be easily accomplished. The surface pressure must be estimated first. At the subsonic flow the exit pressure will be atmospheric. If the flow is sonic the pressure will be greater than atmospheric. A sample calculation is given by Hawkins et al. (1980). The case of two-phase flow, gas-condensate and oil, must be considered (Hawkins et al., 1981). A pressure less than the bubble point pressure may be reached in the reservoir; in that case, an empirical formula must be used. Flow-string resistance for simultaneous oil, gas, and water flow can be estimated using one of the numerous correlations available for that purpose (Brill and Beggs, 1978). For example, the Poettmann and Carpenter (1952) correlation considers one flow regime and no slip, i.e., liquid and gas are traveling up the well at the same velocity. The Hagedorn and Brown (1965) correlation accounts for both slip and multiple flow regimes. Typical flow regimes are bubble flow, slug flow, transition flow, and mist flow. A recent work (Reinicke et al., 1987) shows that the Hagedorn and Brown correlation gives the best results although the correlation is less sophisticated than the others. The downhole well pressure is then computed for various flowrates. 11.2.3. Crossplots

When the formation resistance and flow-string resistance curves are plotted on the same graph, the intersections give both the probable flowrate and the downhole pressure. Figures 11-1and 11-2 are typical crossplots for gas blowouts. Figure 11-3 shows a typical crossplot for two-phase flow conditions. If the permeability is not known, then several values may have to be used to get a range of possible well pressures and flowrates. These figures illustrate the large differences that may be encountered when using the various correlations in two-phase flow.

11.3. BLOWOUT CONTROL

A review of relief well kill procedures was carried out by Flak and Goins (1984). Four techniques are described: water flooding kills, dynamic kills, overbalance kills, and high-rate production kills. 11.3.1. Waterflooding kills

One technique used especially in high-permeability formations (>500 mD) consists of (i) prekilling the blowout by flooding the formation with water; (ii) when

RELIEF WELL ENGINEERING TO CONTROL BLOWOUTS

323

FLOW RATE ( x 1000 STBO / D A Y

Fig. 11-3. Example of crossplot of formation and flowstring resistance in two-phase flow. The various correlations provide different solutions. The Hagedorn and Brown correlation gives the best results (after Hawkins et al., 1981).

the blowout is producing 100% water, injecting mud by fracturing the formation, thus terminating the kill operation. This technique was used successfully by Shell during the 1970-1971 Bay Marchand fire (Miller and Clements, 1972). The injection operation was simulated with a simple computer model based on Darcy's law for radial flow of an incompressible fluid. According to the results of this simulation, it is important not to fracture the formation during the flooding phase since such a fracturation would create a direct path to the blowout well, making the kill operation impossible (Lehner and Williamson, 1974). One concern in the Bay Marchand case was the high overbalance pressure required during drilling and cementing the blowout zone in the relief well. Actually, this high overbalance pressure did not cause problems. Hence the conclusions are: (i) since a large overbalance is generally permissible, circulation cannot be lost in the relief well unless it intersects the blowout well; (ii) the flow of water from the relief well is basically radial; (iii) at breakthrough, high production rates will cause the oil to cusp into the side opposite the blowout for an appreciable period; (iv) mud fracturation is required as a final step to create a direct path to the "wild" well and control abnormal formation pressures. Of the eleven wells on fire in Bay Marchand, eight were controlled without significant problems, two with great difficulty, and one had to be controlled by surface operations. The success of the technique is highly dependent on the distance between the blowout well and relief well, which should be less than 18 ft (5.5 m). Other factors, including permeability barriers, anisotropy, and too large an injection

324

R. DESBRANDES

thickness, may prevent a successful kill. In addition to this particular example, this method has been used successfully for other blowouts (Barnett, 1977). 11.3.2. Dynamic kills

The dynamic kill technique involves killing a well by injecting a fluid through a communication link and up the blowout annulus at such a rate that the static formation pressure is exceeded and the formation stops producing (Blount and Soelinah, 1981). Multiphase flow occurs during the kill and single phase immediately after. The flowrate must be maintained such that the sum of the frictional and hydrostatic pressures exceeds the static formation pressure until a heavier kill mud can replace the lighter dynamic kill fluid. Figure 11-4 shows the principle of dynamic kill. In the relief well, the downhole pressure must be monitored and maintained at about formation pressure. A small tubing full of water is used for monitoring the pressure. The annulus of the relief well is used for injection. Figure 11-5 shows the typical variation of the formation gas production versus the flowing bottomhole

-

P l w = BHP Waterhead + PI NoControl Pan = EHP - Ph,d. PI (WHP = 0)

Q Relief Well Annulus

-

-3STubing

-Static water

-.

Blowout

Well

(58.62 MPa) 85Oopsi

Relief valve

Positive choke

-1

BHP = WHP +

/ Pn,, +PI

1 7,100 ( 4 9 . 9 6 M P a ) PSI Reservoir

Fig. 11-4.Principle of dynamic kill. The high water Rowrate injected in the blowout generates a pressure loss sufficient to kill it. The relief valve in the figure represents the formation fracturation pressure not to be surpassed (after Blount and Soelinah, 1981).

RELIEF WELL ENGINEERING TO CONTROL BLOWOUTS

325

MPa

FLOWING BOTTOMHOLE P R E S S U R E ( p s i x 103)

Fig. 11-5. String and formation resistance curves for a dynamic kill. The two-phase string resistance shows a minimum pressure as the gas flowrate increases for a constant water injection.

pressure for various water injection flowrates. In this case a water flowrate of 80 barrels per minute (0.212 m3/s) will be sufficient to kill the well and, with zero gas flowrate, the water injection rate can be cut back to 70 bbl/min (0.185 m3/s). In contrast to the water-flooding technique, the communication link used in the dynamic kill is produced by fracturing and “acid worming”. Acid worming is achieved by injecting hydrochloric acid into limestone formations. The two wells must be as close as possible to provide the least pressure drop in the link. This technique can also be used to control a cased blowout by targeting the relief well to contact the wild well and establishing the link by jet perforating. Several blowouts have been killed successfully using dynamic kill (Wiryodiarjo et al., 1982). 11.3.3. Overbalance kills

Overbalance kill is the procedure that most relief well kill attempts have followed in the past. A communication is established by fracturing the formation with a light fluid. Subsequently, a fluid of sufficient density to control (overbalance) the reservoir pressure is pumped into the blowout at a rate high enough to overcome the reservoir flow; then cement is pumped into the well to complete the kill. The major difficulty is injecting the dense fluid at a high enough rate without fracturing the formation around the relief well and losing the mud. This technique is essentially a crude dynamic kill. The modern dynamic kill approach has many advantages over the overbalance kill.

326

R. DESBRANDES

11.3.4. High-rateproduction kills

If salt water is produced with the oil or gas in the wild well, it may be possible to complete the relief well in the blowout formation and produce it at a very high rate, developing a low-pressure zone that intercepts the blowout formation and draws salt water by coning. In this case, the blowout will kill itself by failing to lift the salt water. This technique has reportedly been used successfully (Flak and Goins, 1984). 11.3.5. Polymer kills Polymer injection has been attempted with success to control the leakoff into the formation and to focus the kill fluid toward the blowout. This technique only works in high-permeability, fractured, or vuggy-type formations. Since blowouts occur most often in these types of formations (Ely and Holditch, 1987), this technique is widely used.

11.4. DIRECTIONAL PLANNING AND TRAJECTORY DESIGN

Relief wells are normally spudded upwind and at a secure distance from the blowout, which means that the horizontal departure to the target well will be 1500 to 3000 ft (460-915 m). Four major types of wellbore trajectories, shown schematically in Fig. 11-6, can be selected: continuous-build, build-and-hold, build-

‘s’ PIPE)

Fig. 11-6. Major types of wellbore trajectories. The most common trajectory is “build-hold-and-drop,” especially when the casing must be contacted (after Bourgoyne et al., 1986).

RELIEF WELL ENGINEERING TO CONTROL BLOWOUTS

327

hold-drop-and-hold (modified “S”), build-hold-and-drop (“S” type) (Bourgoyne et al., 1986, p. 351). The preferred trajectory is the build-hold-and-drop type. Unless the blowout trajectory is known, a first build-and-hold relief well is drilled to go past the blowout. The distance and orientation of the blowout is determined at the nearest point. After plugging back, a sidetrack is drilled from the drop portion of the relief well. Often several sidetracks are necessary, especially if a contact or mill-through is required (Grace, 1985).

11.5. DIRECTIONAL SURVEYING

Directional surveying includes directional measurements, trajectory calculation and accuracy estimates. Directional measurements include: single shots and multishots, steering tools and MWD (measurement-while-drilling),and north seekers. The progress in this area over the last few years is mainly due to the use of advanced sensors and computers. 11.5.1. Single shots and multishots Devices for measuring the inclination and orientation of the borehole, which take downhole photographs of a pendulum and of the face of a magnetic compass or gyroscope, were exclusively used before 1970. They are still used today due to their low cost. Non-magnetic drill collars are required for the magnetic measurements. The single-shot instrument takes one photograph (shot) either for inclination control in regular drilling operations or for orienting the bottomhole assembly during directional drilling. The multishot can take up to 1000 photographs while the drill string is being pulled out (Bourgoyne et al., 1986, p. 377). The gyroscope data require a tedious and complex interpretation. To alleviate this difficulty, computerized gyroscopes, operated on electric wireline, can supply on-the-spot directional data and trajectory calculations (Guillory, 1978). 11.5.2. Steering tools and MWD

Steering tools and MWD techniques use the same type of instrument package. Three servo-controlled accelerometers are used to measure the inclination of the well, and three single-axis magnetometers are used to measure the earth’s magnetic field orientation (Russell, 1970). The six data measured are used in a computer program to determine the inclination, the orientation with respect to magnetic north, the tool face if a bent sub is used, and the possible magnetic perturbations, especially drill collar perturbations (Russell and Russell, 1979; Grinrod and Wolff, 1983). The measurements are usually carried out during drilling. Multishot-type devices using accelerometer/magnetometer packages and digital recording are now available to replace the conventional multishots (Gust, 1986).

328

R. DESBRANDES

11.5.3. North seekers Rate gyroscopes are instruments that measure the rate of absolute rotation around a sensitive axis. In the borehole they detect the earth’s rotation vector and, consequently, are immune to any magnetic perturbation. Two systems are presently used: single-axis gyroscopes rotated slowly, and two- or three-axis stationary gyroscopes (strapped down) to determine the earth’s rotation vector. In both instances the housing of the instrument must be perfectly still in the borehole while station measurements are made. As the platform containing the single-axis gyro rotates slowly along the borehole axis, the gyro will sense the maximum signal when its sensitive axis is lined up with the geographic north. An accelerometer mounted on the same platform will sense the maximum signal when its sensitive axis is in the vertical plane. The borehole orientation can then be calculated from the phase difference between the two signals (Wright, 1983). In a three-axis gyroscope system, each sensitive axis measures one rotation component. The three components can be used to define a vector, the earth’s rotation vector, located in the north vertical plane. This vector can be used in lieu of the magnetic field vector in a steering tool or MWD computer-type program if accelerometer measurements are available (Gibbons and Hense, 1987). It should be noted that each measurement is made with respect to geographic north with no perturbation possible. Other gyroscope-type measurements can be made using inertial platforms. One of these uses a two-axis gyroscope and a two-axis accelerometer (Camden et al., 1981), the other is a regular aircraft platform (Morgan, 1979). This second instrument makes displacement measurements in 3-D and defines the trajectory without using inclination, azimuth, or well depth. 11.5.4. Trajectory calculation

Many algorithms are used for trajectory calculation. The three most common are: the tangential method, the average angle method, and the minimum curvature method (Bourgoyne et al., 1986, p. 362). In the tangential method it is assumed that for each survey station, inclination and orientation angles remain constant over the preceding course length. The corresponding horizontal departures and true vertical depth are readily calculated. A summation leads to the total north/south and east/west coordinates as well as total vertical depth. The average angle method is similar, but the angles considered are the average values of the angles measured at the beginning and at the end of a course length increment. This method eliminates part of the sizeable error caused by not considering the previous inclination and direction. The minimum curvature method uses the angles at both ends of the increment and assumes a curved wellbore tangent to the vectors defined by the inclination angles at each end. This method is one of the most accurate. Many other methods

RELIEF WELL ENGINEERING TO CONTROL BLOWOUTS

329

have been used commonly but with only a minimal accuracy improvement. The accuracy depends also on the distance, which should not exceed 100 ft (30 m), between survey points. Since the best possible accuracy is required for a successful relief well operation the minimum curvature method should be used. 11.5.5. Accuracy models

Since the relief well must sometimes physically intersect the blowout, trajectory accuracy is very important in relief well engineering. Two approaches are currently in use: the probability model, and the systematic error model. The probability model is based on the assumption that inclination and azimuth angle errors are uniformly distributed between two limits. Furthermore, there is no correlation between the errors recorded at different stations (Walstrom et al., 1969). With this model the uncertainty ellipses can be calculated to define a numerical probability of the hole being located at a certain distance from the calculated position. Figure 11-7 shows the ellipses for a highly deviated hole at a total depth of 5400 ft (1646 m). The same results can be obtained by adding an algorithm of Monte Carlo simulation of error to the station data. The ellipses can be defined by running the trajectory calculation many times. The small dimension of the ellipse for 0.999 certitude is striking and does cast some doubt on the method.

rn

- 740 2420:

4a

C

E

2400:

-730 2380

2360

{

720

Fig. 11-7. Ellipses of uncertainty of bottomhole position for a 5400-ft borehole. The calculated position is at the center of the ellipses. The probability of the true position is indicated for each ellipse (after Walstrom et al., 1969).

330

R. DESBRANDES 300

I

w-

1 I-

a

J W

K

I 0

,

,

,

I

I

I

I

,

]

30 40 50 60 7 0 00 90 A V E R A G E HOLE INCLINATION ( Degrees 1 10 20

Fig. 11-8. Spical lateral position uncertainties of magnetic and gyroscopic surveys. A “good” gyroscope survey is better than a “good” magnetic survey for deviations less than 70”; above that point, the magnetic survey is better (after Wolff and de Wardt, 1981).

The systematic error model (Wolff and de Wardt, 1981) suggests that the errors in a particular survey are systematic and leads to a total error larger by a factor of f i than the Walstrom model error (n being the number of stations). Taking into account the typical error values for good or poor surveys, Wolff and de Wardt (1981) computed the lateral position uncertainty shown in Fig. 11-8. They also define radial and vertical uncertainties that are smaller for the same set of directional data. This worhpplies to multishot-type measurements. For the accelerometer-magnetometer or rate-gyroscope type of measurements, a new method has been proposed recently that takes into account errors in the raw vector component data (Holmes, 1987). The method is based on the observation that, although errors exhibit a Gaussian distribution, they are also highly correlated from one survey station to the next. Limited results are currently available.

11.6. BLOWOUT WELL DISTANCE FROM RELIEF WELL

Frequently, when a well is out of control, no directional data are available. Consequently, the bottomhole position is not known, and, even with state-of-the-art directional measurements in the relief well, ranging techniques are necessary to locate the wild well. With steel in the borehole, drill pipes and/or casing, three

331

RELIEF WELL ENGINEERING TO CONTROL BLOWOUTS

methods are applicable: electrical, active electromagnetic, and passive electromagnetic. For a “clean” borehole (i.e., metal-free) only acoustic noise recording is currently available. 11.6.1. Electrical method

The electrical method uses the Ultra-Long Spaced Electric Log (ULSEL) technique (Runge et al., 1969) and was originally designed to detect and map the profile of salt domes and other large resistive anomalies. Here the technique is used for detecting conductive casings. Basically, the electric sonde is a very long “normal”, with the typical electrode arrangement on the insulating bridle being A-75’-M175’-M2-200’-N-350’ cable armor (A-22.86 m-MI-22.86 m-M2-60.96 m-N-106.68 m cable armor) (Haanschoten, 1977a, b). This arrangement is labeled 75/350 or 150/350in the literature. In order to calculate the expected resistivity in an infinite tabular formation, measurements made with short-spacing resistivity sondes are necessary. The resistivity measured with the ULSEL spacings is then compared with the expected resistivity. When a conductive casing is in the vicinity, the ULSEL-measured resistivity is a function of the distance of the casing, approach angle, resistivity values and casing size. Charts have been calculated for various conditions (Mitchell et al., 1972). Figure 11-9 shows typical curves for 75- and 150-ft (22.86 and 45.73 m) “normal” resistivity measurements. A field example of ULSEL resistivity measurements is presented in Fig. 11-10. The distance has been determined using the resistivity ratio and the response curve “150/350 normal” shown in Fig. 11-9. Although this analysis does not give the direction of the blowout casing with respect to the relief well, the technique has been widely used with success for distance determination. m 10

5

0 l.Or

15

20

I

I

I

25

I

30

11

I

BASIS I. FORMATION RESIST.6 Om (HORIZ.)

2. RESIST. VERT./HORIZ. = 1.5 3. VERTICAL ANGLE = 4 DEGREES

4

I I

I

1

I

I

1

1

I

i

332

R. DESBRANDES R E S I S T I V I T Y , Ohm- meters

0 2720

10 20

d (ft.) 30 40 50 60

I

2730

-L

I 2740

+ a W

n 2750

2760 L

0

5

10

15

2

d (ml

Fig. 11-10, Example of an ULSEL survey near a casing and its interpretation. The expected values have been computed from a deep investigation resistivity log to average for the various resistivities of the strata included in the long spacing. The distance is computed with the data of Fig. 11-9.

11.6.2. Active electromagnetic method This method is similar to the electrical method but the alternating magnetic field generated by the current flowing in the casing is measured instead of the electric potential. Figure 11-11 shows the current emitted by electrode A. The magnetometer, located in M at 300 ft (91.44 m) below the current electrode in the relief well, measures the magnetic field induced by the casing current (West et al., 1983). The intensity of the field is related to the distance between the blowout and the relief well. The direction given by the three magnetic components is at 90" from the blowout direction according to the Biot-Savart law. Amplitude measurements are shown in Fig. 11-12. The technique has been used with success to intersect a blowout at 16,053 ft (4893 m) (Grace, 1985).

11.6.3. Passive magnetic method Due to inspection and manufacturing processes, the casing is usually magnetized. A typical magnetization pattern is shown in Fig. 11-13 (Robinson and Vogiatzis, 1972). A sonde equipped with four magnetometers has been built for detecting the magnetism of the casing up to 100 ft (30.5 m) away in the presence of the earth's magnetic field (Morris and Costa, 1977; Morris et al., 1978). A vertical gradient, which is a function of distance and independent of the earth's magnetic field, is measured. Radial measurements of two magnetic components at 90°, when stripped of the earth's magnetic field, give the direction of the blowout. Figure 11-14 is a sketch

RELIEF WELL ENGINEERING TO CONTROL BLOWOUTS

333

S U R FA C E

-BLOWOUT

)”: c

-

L

c

c

- IWNI RREL ELINE IE F

WELL

WELL

c

-d CURRENT FLOW IN PIPE

I

1 \

f

c

/

CURRENT EMITTED INTO THE GROUND

M

Z Fig. 11-11. Current flow in the casing of blowout well due to the current emitted by an electrode. The current flow in the casing is nu1 at the electrode depth and increases then decreases as more current is emitted than received by the casing. The current pattern is symmetrical both upward and downward (after West et al., 1983).

of the Magrange I1 logging tool (Desbrandes, 1985, p. 453). The illustration of a typical recording of the vertical gradient shown in Fig. 11-15, indicates a dipole and a monopole and includes a schematic interpretation (Morris and Costa, 1977; Morris et al., 1978). The passive magnetic technique has been used widely with good results.

11.6.4. “Clean” borehole methods In a “clean” borehole (one containing no steel), magnetic or electrical techniques cannot be used. Acoustic noise measurements are the sole possibility. A sensitive microphone is lowered into the borehole and the frequency spectrum of the noise is recorded at various depths (McKinley et al., 1973; Britt, 1976). Maximum amplitudes are recorded at the nearest point to the blowout well. No published information relates the application of this measurement to blowout well distance ranging although this technique has been used. An estimate of the noise source

334

R. DESBRANDES

2200 Legend

*

Run 1 Run2. o Run 3 - 0

a a

g

600j

$

300

:*.

z

1i J

g o

I

200-

2

v,

100

7500

7000

8000 8500 9000 ALONG HOLE DEPTH, Ft

9500

10000

Fig. 11-12. Field data showing the alternating magnetic field intensity near a casing. With this data the distance and the direction of the casing of the blowout well can be calculated (after West et al., 1983).

COLLA(I END

a

THREAD E N 0

RADIAL M A G N E T I C FIELD AT

3/Ain , G A U S S

Fig. 11-13. A typical example of the radial magnetic field exterior to a long casing joint: (a) schematic form; (b) intensity 3/4" away from the casing. Magnetization will differ from casing to casing according to the manufacturing, handling, and inspection procedures (after Robinson and Vogiatzis, 1972).

RELIEF WELL ENGINEERING TO CONTROL BLOWOUTS

335

magnetometer

I Fig. 11-14. Schematic diagram of the Magrange I1 logging tool. The sketch shows the two axial magnetometers to measure the field axial gradient and the two radial magnetometers to determine the direction of the blowout well with respect to the relief well (after Desbrandes, 1985).

intensity can be made if the flowrate in the blowout well is known. According to R.M.McKinley (pers. commun., 1987) and E.L. Britt (pers. commun., 1987) the amplitude decreases approximately with the square of the distance up to 100 ft (30.5 m); thus, the distance, but not the direction, can be estimated. Acoustic noise logs are also used for making sure that the wild well is definitely killed and that no underground flow is persisting (Bruist, 1972). Until new technologies become available only cased wells or wells containing drill strings can be located with certainty.

11.7. BLOWOUT EXAMPLES

11.7.1. Cox et al. No. 1

Cox et al. No. 1, an exploratory well, near Jackson, Mississippi, blew out at 21,122 ft (6438 m) in the Smackover on March 25, 1970 while a trip out of the hole with a core was being made (Bruist, 1972). Cox No. 2 was spudded and planned with a

P

o \

w w

RELIEF WELL ENGINEERING TO CONTROL BLOWOUTS

337

21.112’ (6.438rn)

Fig. 11-16. Diagram of the proposed relief wells to kill Cox No. 1. Cox No. 4 reached its target first and was used to kill Cox No. 1 (after Bruist, 1972; courtesy of Journal of Petroleum Technology).

“build-and-hold” trajectory to intersect the blowing well at the bottom. A second well, Cox No. 4, was also spudded to intersect Cox No. 1 at 10,000 ft (3048 m), as shown in Fig. 11-16. This last well reached its target first and was directed to contact the wild well casing with the ULSEL technique and magnetostatic measurements. Two sidetracks were necessary. Interwell communication was established at 10,550 ft (3216 m) by jet-perforating, and the well was killed with a heavy cement slurry. The kill was confirmed with a noise-temperature survey. 11.7.2. Bergeron No. 1

R.L. Bergeron No. 1 was being drilled in the Tuscaloosa Trend near Baton Rouge, La., when it blew out at 18,562 ft (5658 m) (Warren, 1981). The relief well, Bergeron No. 2, was planned as shown in Fig. 11-17. The Bergeron No. 1trajectory was known within a 32 ft (9.75 m) radius. Then Bergeron No. 1 bridged and died. A noise survey was run in Bergeron No. 2 to make sure that no underground flow was taking place.

338

R. DESBRANDES

I' 4

-DRILL STRING

Fig. 11-17. Schematic of relief well Bergeron No. 2 with the detail of the casing design. Contact was established as shown, but Bergeron No. 1 bridged and died before a communication could be attempted. A noise survey run in Bergeron No. 2 indicated that no flow was taking place (after Warren, 1981; courtcsy of Journal of Petroleum Technology).

11.7.3. Arun Field well No. CII-2

Well No. CII-2 in Indonesia's Arun Field blew out during drilling operations at 9650 ft (2941 m) on June 4, 1978 (Blount and Soelinah, 1981). Two relief wells were spudded as shown in Fig. 11-18 (Leonard, 1979). Relief well CII-8 reached the formation first. Accurate directional data and magnetostatic surveys indicated that the wells were less than 50 ft (15.24 m) apart. A communication link was produced by acid worming and fracturing. The dynamic kill technique was used to control the wild well with 85 bbl/min (0.225 m3/s) of water, followed by intermediate mud of 14.5 ppg (1737 kg/m3) at 30 bbl/min (0.079 m3/s). Finally, a 16.5 ppg (1977 kg/m3) mud was injected to complete the kill.

RELIEF WELL ENGINEERING TO CONTROL BLOWOUTS

339

/*

/

1 Fig. 11-18. Schematic diagram of the two relief wells spudded to kill well Arun (211-2. CII-8 reached its target first, less than 60 ft (18.3 m) away from (211-2. A dynamic kill was used to control CII-2 after a communication was established (after Leonard, 1979; courtesy of Oil and Gas Journal).

11.8. CONCLUSIONS

Relief well drilling is mandatory when a deep blowout occurs since there is no guarantee that the well will bridge and the blowout will die. Even if bridging does occur, an underground blowout may still be in progress. In any well, a reliable borehole trajectory survey should be made when highpressure zones are suspected and a blowout is possible. This strategy prevents long and costly ranging operation to locate the blowout well. Measurement-while-drilling (MWD) techniques provide excellent trajectory control of the relief well, allowing the target to be reached precisely and efficiently. Today’s ranging technology defines the distance and direction of the blowout with an accuracy that permits casing contact if necessary. However, ranging problems still persist when the borehole does not contain magnetic material. Several kill techniques have been developed and applied with success. In several of these applications, the blowout well was salvaged. Acoustic noise logs are often used as final confirmation that the blowout well has been definitively killed.

340

R. DESBRANDES

REFERENCES Barnett, R.D., 1977. A logical approach to killing an offshore blowout: West Cameron 165, Well No. 3, Offshore Louisiana. SPE 6903, SOC.Pet. Eng. Annu. Fall Meet., Denver, Colo., October 9-12. Beggs, H.D. and Brill, J.P., 1973. A study of two-phase flow in inclined pipes. J. Pet. Technol., 25 (4): 607-617. Blount, E.M. and Soelinah, E., 1981. Dynamic kill: controlling wild wells a new way. World Oil, 193 (5): 109-126. Bourgoyne, A.T., Jr., Millheim, K.K., Chenevert, M.E. and Young, ES., Jr., 1986. Applied Drilling Engineering. SPE Tatbook Series, Vol. 2. Richardson, Texas, 502 pp. Brill, J.P. and Beggs, H.D., 1978. Two-phase Flow in Pipes. University of W s a , 'hlsa, Okla., 480 pp. Britt, E.L., 1976. Theory and application of the borehole audio tracer survey. Paper BB, SOC.Prof: Well Log Analysts Symp., Denver, Colo., June 9-12. Bruist, E.H., 1972. A new approach in relief well drilling. J. Pet. Technol., 24 (6): 713-722. Camden, D.J., Gartner, J.E. and Moulin, P.A., 1981. A new continuous guidance tool used for high accuracy directional survey. SPE 10057, SOC.Pet. Eng. Annu. Fall Meet., San Antonio, Texas, October 5-7. Desbrandes, R., 1985. Encyclopedia of Well Logging. Gulf Publishing, Houston, Texas, 584 pp. Ely, J.W. and Holditch, S.A., 1987. Conventional and unconventional kill techniques for wild wells. SPE 16674, SOC. Pet. Eng. Annu. Fall Meet., Dallas, Texas, September 27-30. Flak, L. and Goins, W.C., 1984. New techniques, equipment improve relief well success. World Oil, 198(1): 113-118. Gibbons, EL. and Hense, U., 1987. A three-axis laser gyro system for borehole wireline surveying. SPE 16679, SOC. Pet. Eng. Annu. Fall Meef.,Dallas, Texas, September 27-30. Grace, R.D., 1985. Case history of Texas' largest blowout shows successful techniques on deepest relief well. Oil Gas L , 83 (20): 68-76. Grinrod, S.J. and Wolff, J.M., 1983. Calculation of NMDC length required for various latitudes developed from field measurements of drill string magnetization. IADCISPE 11382, MDC/SPE Drill. Conf., New Orleans, La., February 20-23. Guillory, C., Jr., 1978. Surface recording gyroscope system saves rigtime. Oil Gas J., 76(19): 186-192. Gust, D.A., 1986. An evaluation of survey accuracy at Cold Lake. Paper 86-37-06, Pet. SOC. of CIM, 37th Annu. Tech. Meet., Calgary, Aka., June 8-11, pp. 75-84. Haanschoten, G.W., 1977a. Logging tool offers greater depth of investigation for relief well. Oil Gas J., 75 (2): 70-74. Haanschoten, G.W., 1977b. Ulscl system performs on Brunei blowout under tough conditions. Oil Gas J., 75 (3): 77-79. Hagedorn, A.R. and Brown, K.E., 1965. Experimental study of pressure gradients occurring during continuous two-phase flow in small diameter vertical conduits. J. Pet. Technol., 17 (4): 475-484. Hawkins, M.F., Bassiouni, Z., Bernard, W.J., Bourgoyne, A.T, Jr., Veasey, M.J. and Whitehead, W.R., 1980. Methods for Determining Vented Volumes During Gas Well Blowouts. Document DOE/ BETC/2215-1, US.Department of Energy, NTIS, U.S. Department of Commerce, Springfield, Va., October, 95 pp. Hawkins, M.F., Bassiouni, Z., Bernard, W.J., Bourgoyne, A.T., Jr., McMullan, J.H., Veasey, M.J. and Whitchead, W.R., 1981. Methods for Determining Vented Volumes During Gas-Condensate and Oil Well Blowouts. Document DOE/BETC-3000-1 (DE81030779), U.S. Department of Energy, NTIS, U S . Department of Commcrce, Springfield, Va., September, 36 pp. Holmcs, A,, 1987. A method to analyze directional surveying accuracy. SPE 16680, SOC.Pet. Eng. Annu. Fall Meet., Dallas, Tcxas, September 27-30. Hughes, V.M., Podio, A.L. and Sepehrnoori, K., 1987. A computer assisted analysis of trends among Gulf Coast blowouts. SPEIIADC 16127, IADC Drill. Conf, New Orleans, La., March 15-18. Lee, J . , 1982. Well Testing. Society of Petroleum Engineers, New York, N.Y. Lehner, F, and Williamson, AS., 1974. Gas-blowout control by water injection through relief wells: a thcorctical analysis. SOC.Pet. Eng. J., 14(4): 321-329. Leonard, J.E., 1979. Single relief well kills Arun blowout. Otl GasJ., 77(2): 73-76.

RELIEF WELL ENGINEERING TO CONTROL BLOWOUTS

341

McKinley, R.M., Bower, EM. and Rumble, R.C., 1973. The structure and interpretation of noise from flow behind cemented casing. J. Pet. Technol., 25 (3): 329-338. Miller, R.T and Clements, R.L., 1972. Reservoir engineering techniques used to predict blowout control during the Bay Marchand fire. J. Pet. Technol., 24(3): 234-240. Mitchell, ER., Robinson, J.D., Vogiatzis. J.P., Pehoushek, F., Moran, J.M., Auburn, B.E. and Berry, L.N., 1972. Using resistivity measurements to determine the distance between wells. 1.Pet. Technol., 24 (6): 723-740. Morgan, D.G., 1979. High accuracy directional surveying of wells employing inertial techniques. SPE 8156, SOC.Pet. Eng. Offshore European Con$, Aberdeen, September 3-7. Morris, EJ. and Costa, J.P., 1977. A new method of determining range and direction from a relief well to a blowout well. SPE 6781, SOC.Pet. Eng. Annu. Fall Meet., Denver, Colo., October 9-12. Morris, F.J., Waters, R.L., Roberts, G.E and Costa, J.P., 1978. New magnetic ranging system pinpoints blowout well location. Oil Gas L , 76 (1 1): 57-62. Podio, A.L., Fosdick, M.R. and Mills, J., 1983a. Study shows incidence of blowouts in southeastern U.S./Gulf of Mexico. Oil Gas 1,81(44): 119-123. Podio, A.L., Fosdick, M.R. and Mills, J., 1983b. Analysis gives blowout causes, trends, costs. Oil GasJ., 81 (45): 125-133. Poettmann, F.H. and Carpenter, P.G., 1952. The multiphase flow of gas oil, and water through vertical flow strings with application to the design of gas-lift installations. Drilling and Production Practice, API, pp. 257-317. Reinicke, K.M., Remer and Hueni, 1987. Comparison of measured and predicted pressure drops in tubing for high-water-cut gas wells. SPE Prod. Eng., 2 (3): 165-177. Robinson, J.D. and Vogiatzis, J.P., 1972. Magnetostatic methods for estimating distance and direction from a relief well to a cased borehole. J. Pet. Technol., 25 (6): 741-749. Runge, R.J., Worthington, A.E. and Lucas, D.R., 1969. Ultra-long spaced electric log (ULSEL). Paper H, SOC.Prof. Well LogAnulysts Symp., Houston, Texas, May 25-28. Russell, M.K., 1970. The design and development of a surface reading orienting survey. Paper 801-46R, API Prod. Div., Pacific Coast District Meet., LQSAngeles, Calif., May 12-14. Russell, M.K. and Russell, A.W., 1979. Surveying of Boreholes. U.S. Patent No. 4, 163,324 (August 7); 7 claims; 7 figs. Walstrom, J.E., Brown, A.A. and Harvey, R.P., 1969. An analysis of uncertainty in directional surveying. J. Pet. Technol., 21 (4): 515-523. Warren, T.M., 1981. Directional survey and proximity log analysis of a downhole well intersection. J. Pet. Technol., 33 (12): 2351-2362. West, C.L. Kuckes, A.F. and Ritch, A.J., 1983. Successful ELREC logging for casing proximity in an offshore Louisiana blowout. SPE 11996, SOC. Pet. Eng. Annu. Fall Meet., San Francisco, Calif., October 5-8. Wiryodiarjo, S., Sumanta, K. and Mustiko, S., 1982. Formation fracturing kills Indonesian blowout. Oil CasJ., 80(46): 115-127. Wolff, C.J.M. and de Wardt, J.P., 1981. Borehole position uncertainty - analysis of measuring methods and derivation of systematic error model. J. Pet. Technol., 33 (12): 2339-2350. Wright, J., 1983. Rate gyro surveying of wellbores in the Rocky Mountains. SPE 11841, SOC.Pet. Eng. Rocky Mountains Reg. Meet., Salt Lake City, Utah, May 23-25.