How can new technology be designed, or existing technology be used in a new way, to improve performance and reduce costs? This is a question every operator asks in an increasingly competitive market. With a successful horizontal development program in the Giddings Field in 1990 and 1991, Texaco's Horizontal Drilling Team searched for answers to this question while expanding the program to the Brookeland Field in Newton Co., Texas. The "Dual Lateral" concept was being used in other areas, but this was the first time Texaco would try this wellbore design - and in a wildcat area. Planning aspects, the drilling operation and subsequent remedial operations will be reviewed. Production results and some conclusions as to the feasibility of drilling the dual laterals will also be presented. INTRODUCTION: The Austin Chalk trend is a fractured carbonate 30 to 35 miles wide and runs from northern Mexico to southern Mississippi. Texaco's East Region onshore horizontal drilling experience began in July 1990 in the Pearsall Field, Frio Co., Texas. In 1991, our efforts were concentrated primarily in the Giddings Field to the northeast in Burleson Co. In 1992, as our efforts continued in the Giddings Field, we also expanded our program further east 'in the trend into the Brookeland Field. The East Region's onshore Exploration and Production Divisions have drilled a total of forty-one (41) horizontal wells as of March 1993: 3 Austin Chalk wells in Pearsall 19 Austin Chalk wells in Giddings 8 Georgetown (fractured carbonate) wells in Giddings 2 Pittsburgh (sandstone) wells in New Hope 8 Dual Lateral Austin Chalk wells in Brookeland 1 Single Lateral Austin Chalk well in Brookeland The Brookeland Field, as stated, is located in Newton Co., Tx. P. 419^
Summary Petro-Hunt Corp. used a unique horizontal-well design to optimize development of an irregularly shaped lease in the Austin Chalk formation in Texas. Two medium-radius horizontal bores were drilled in opposite directions from one vertical hole to maximize horizontal displacement in the lease. Underbalanced drilling techniques were used to prevent formation damage. The well design resulted in a significant cost savings per horizontal foot compared with 24 offset wells that the operator drilled. This paper reviews well planning and drilling and emphasizes techniques used to intersect thin horizontal targets and to initiate the second horizontal bore. Production results and drilling economics are discussed briefly, and ideas on future dual-horizontal-well applications are presented. Introduction Austin Chalk Formation. The literature presents1–3 many descriptions of the Austin Chalk formation in Texas. For this paper, the formation is characterized as a dense, amorphous, Cretaceous limestone often found to contain intebedded and sometimes marly shale streaks. Fig. 1 shows a trend map of this oil-bearing formation. In the past, the low matrix porosity and low permeability of the Austin Chalk formation limited the economical development of its hydrocarbons to those areas where a vertical well had a reasonably good chance of penetrating a naturally occurring vertical fracture system. These fracture systems are most extensive when associated with local faults or anticlines.2 The presence of vertical fractures in this otherwise tight formation makes it ideal for horizontal drilling. Since 1985, drilling of horizontal wells has become increasingly more popular than vertical wells for improving the success rate in previously developed areas of the Austin Chalk formation. Horizontal drilling also is used to explore areas considered too risky for vertical wells because of the sparseness of the local fracture systems. Continued improvements in horizontal drilling technology caused Austin Chalk drilling to reach "boom" levels in early 1990. Although some horizontal wells drilled in the Austin Chalk have been completed with slotted liners or casing, the openhole completion method is preferred. The high mechanical integrity of the Austin Chalk is conducive to openhole completions. Advantages to this method include (1) low initial costs, (2) little potential for mechanical problems, (3) more options than other methods for recompletion or remedial work, and (4) minimal flow restriction.4 The Pearsall Field, located 70 miles southwest of San Antonio, supported prolific levels of horizontal drilling activity in 1990–91. Pearsall Partners (Petro-Hunt Corp. of Dallas is managing partner) participated in the drilling of 25 horizontal wells in this field during 1990. The subject of this paper, McDermand Well No. 1, was the 15th well in this series. McDermand Well No. 1. Pearsall Partners operated McDermand Well No. 1; other working interest owners were GLG Energy LP, Austin, and WCS Oil & Gas Corp., Dallas. Located in Frio County, the well is in the southern one-half of the Pearsall field. The targeted pay zone was Interval B1 of the Austin Chalk formation. Interval B1 is a particularly clean, brittle, limestone interval likely to contain microfracture systems. Interval B1 was expected to lay ˜130 ft below the top of the Austin Chalk formation. Penetration of a gas cap or a water boundary was not anticipated. The geologist assigned a horizontal target tolerance of ±10 ft true vertical depth (TVD) to the prognosis depth. An openhole completion would be used on the well. Two primary factors that influenced well planning were lease geometry and fracture orientation. Fig. 2 depicts the lease geometry. The predominant fracture orientation in that part of the field paralleled the north 40° east formation strike. Offset-well data indicated local formation dip to be 1.6° to the southeast. The following criteria were established as necessary to optimize lease development.Maximize horizontal length.Drill perpendicular to the fracture orientation.Allow adequate directional control to keep the wellbore within the lease "hard" lines.Minimize drilling, completion, and production costs. Minimizing costs could be accomplished best by drilling only one well on the lease. Furthermore, field rules stipulated that a second well drilled on the lease would have to be at least 1,200 ft from the original well at all points in the pay zone. Maximizing horizontal length while drilling perpendicular to the fracture orientation would require a northwest-southeast horizontal-well orientation and also would require drilling into the narrow "panhandle" in the northwest lease quadrant. This plan would allow for up to 5,700 ft of horizontal displacement. Two concerns were raised with this plan.Was it reasonable to expect to achieve 5,700 ft of displacement without encountering significant drilling problems? Then, the most displacement ever achieved in the Austin Chalk formation was ˜4,600 ft.Could the well azimuth be controlled adequately, without excessive orientation, to permit passage through the narrow panhandle neck and to keep the wellbore from walking out of the legal lease boundaries? An unusual well plan evolved to address both concerns. The surface location would be placed near the narrow panhandle neck, and a vertical hole would be drilled down to the kickoff point. From there, two opposing horizontal bores, "wings," would be drilled. One wing would be drilled downdip, perpendicular to the fracture orientation, to the southeast. The second wing would be drilled nearly opposite to the northwest. (Lease geometry would prevent us from drilling the northwest wing exactly perpendicular to the fracture orientation.) It was suggested that this well plan also might produce an additional benefit that had not been considered previously. Producing through two intermediate-length horizontal wings instead of one long bore might result in lower bottomhole flowing pressures and higher production rates. Ref. 5 presents a mathematical investigation of this theory. Well Planning Drilling Rig. A triple-derrick drilling rig, rated to 9,000 ft with 4 1/2-in. drillpipe, was selected. The rig was fitted with a 1,000-HP drawworks and two 800-HP triplex pumps. Austin Chalk Formation. The literature presents1–3 many descriptions of the Austin Chalk formation in Texas. For this paper, the formation is characterized as a dense, amorphous, Cretaceous limestone often found to contain intebedded and sometimes marly shale streaks. Fig. 1 shows a trend map of this oil-bearing formation. In the past, the low matrix porosity and low permeability of the Austin Chalk formation limited the economical development of its hydrocarbons to those areas where a vertical well had a reasonably good chance of penetrating a naturally occurring vertical fracture system. These fracture systems are most extensive when associated with local faults or anticlines.2 The presence of vertical fractures in this otherwise tight formation makes it ideal for horizontal drilling. Since 1985, drilling of horizontal wells has become increasingly more popular than vertical wells for improving the success rate in previously developed areas of the Austin Chalk formation. Horizontal drilling also is used to explore areas considered too risky for vertical wells because of the sparseness of the local fracture systems. Continued improvements in horizontal drilling technology caused Austin Chalk drilling to reach "boom" levels in early 1990. Although some horizontal wells drilled in the Austin Chalk have been completed with slotted liners or casing, the openhole completion method is preferred. The high mechanical integrity of the Austin Chalk is conducive to openhole completions. Advantages to this method include (1) low initial costs, (2) little potential for mechanical problems, (3) more options than other methods for recompletion or remedial work, and (4) minimal flow restriction.4 The Pearsall Field, located 70 miles southwest of San Antonio, supported prolific levels of horizontal drilling activity in 1990–91. Pearsall Partners (Petro-Hunt Corp. of Dallas is managing partner) participated in the drilling of 25 horizontal wells in this field during 1990. The subject of this paper, McDermand Well No. 1, was the 15th well in this series. McDermand Well No. 1. Pearsall Partners operated McDermand Well No. 1; other working interest owners were GLG Energy LP, Austin, and WCS Oil & Gas Corp., Dallas. Located in Frio County, the well is in the southern one-half of the Pearsall field. The targeted pay zone was Interval B1 of the Austin Chalk formation. Interval B1 is a particularly clean, brittle, limestone interval likely to contain microfracture systems. Interval B1 was expected to lay ˜130 ft below the top of the Austin Chalk formation. Penetration of a gas cap or a water boundary was not anticipated. The geologist assigned a horizontal target tolerance of ±10 ft true vertical depth (TVD) to the prognosis depth. An openhole completion would be used on the well. Two primary factors that influenced well planning were lease geometry and fracture orientation. Fig. 2 depicts the lease geometry. The predominant fracture orientation in that part of the field paralleled the north 40° east formation strike. Offset-well data indicated local formation dip to be 1.6° to the southeast. The following criteria were established as necessary to optimize lease development.Maximize horizontal length.Drill perpendicular to the fracture orientation.Allow adequate directional control to keep the wellbore within the lease "hard" lines.Minimize drilling, completion, and production costs. Minimizing costs could be accomplished best by drilling only one well on the lease. Furthermore, field rules stipulated that a second well drilled on the lease would have to be at least 1,200 ft from the original well at all points in the pay zone. Maximizing horizontal length while drilling perpendicular to the fracture orientation would require a northwest-southeast horizontal-well orientation and also would require drilling into the narrow "panhandle" in the northwest lease quadrant. This plan would allow for up to 5,700 ft of horizontal displacement. Two concerns were raised with this plan.Was it reasonable to expect to achieve 5,700 ft of displacement without encountering significant drilling problems? Then, the most displacement ever achieved in the Austin Chalk formation was ˜4,600 ft.Could the well azimuth be controlled adequately, without excessive orientation, to permit passage through the narrow panhandle neck and to keep the wellbore from walking out of the legal lease boundaries? An unusual well plan evolved to address both concerns. The surface location would be placed near the narrow panhandle neck, and a vertical hole would be drilled down to the kickoff point. From there, two opposing horizontal bores, "wings," would be drilled. One wing would be drilled downdip, perpendicular to the fracture orientation, to the southeast. The second wing would be drilled nearly opposite to the northwest. (Lease geometry would prevent us from drilling the northwest wing exactly perpendicular to the fracture orientation.) It was suggested that this well plan also might produce an additional benefit that had not been considered previously. Producing through two intermediate-length horizontal wings instead of one long bore might result in lower bottomhole flowing pressures and higher production rates. Ref. 5 presents a mathematical investigation of this theory. Drilling Rig. A triple-derrick drilling rig, rated to 9,000 ft with 4 1/2-in. drillpipe, was selected. The rig was fitted with a 1,000-HP drawworks and two 800-HP triplex pumps.
Petro-Hunt Corporation drilled a horizontal well in the Austin Chaikin Gonzales County, Texas. A high-angle pilot hole was used to determine a target interval and horizontal borehole orientation, while satisfying a variety of operational and geological considerations. The well was directionally drilled to an angle of 44° and intermediate casing was set. The pilot hole was then drilled at the same angle through the target formation and evaluated using openhole logs, including a circumferential acoustic imaging device. After evaluation, the pilothole was plugged back, and the horizontal borehole was kicked off and drilled to a horizontal displacement of 3, 578 ft. This method allowed the entire target formation to be evaluated prior to committing the wellbore to a particular interval, while avoiding potential operational problems associated with a vertical pilot hole. The acoustic imaging log allowed the operator to select the optimum Stratigraphic interval in which to locate the horizontal borehole, and confirmed the proper borehole orientation. The well was successfully completed on schedule and within budget. The planning and drilling of the well is reviewed, with emphasis placed on operational and geological considerations and the evaluation of the pilot hole.
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