Your account already exists. Please login first to continue managing your settings.
An aggressive drilling program anchored by rotary steerable systems (RSS) has paid off in Eagle Ford.
Operating companies are continuously searching for higher rates of return. In newly developed unconventional shale plays like the Eagle Ford, unconventional methods are beginning to reduce drilling time, thereby decreasing costs overall.
Introducing RSS to unconventional resources
Working closely with Weatherford, Swift Energy has applied RSS technology in a horizontal drilling program that has benefitted both sides of the cost-per-barrel equation by reducing drilling time and overall cost per well. In late 2008, Swift undertook a new program to experiment with horizontal wells and multistage completions. The first challenge was to determine whether horizontal drilling was a viable solution, first for the Olmos and then the Eagle Ford formations. Initial wells would be drilled conventionally, with mud motors to drill the curve, then RSS to drill the laterals. If this method proved viable, Swift would then turn to more aggressive applications of RSS, with the thought of changing the way wells in this area are drilled.
|Testing steerable viability in the Olmos sands|
For the first four wells, drilled in the Olmos sand, the typical well configuration consisted of telescoping hole sizes of 36 in. drilled to 90 ft (27 m), 20 in. drilled to 435 ft (133 m), 143?4 in. drilled to 5,500 ft (1,676 m), 97?8 in. drilled to 10,750 ft (3,277 m), and 83?4 in. drilled to 70 degrees of angle in the build section, with 75?8-in. casing set at approximately 12,500 ft (3,810 m), and a 61/8-in. hole drilled to TD of 16,000 ft (4,877 m).
Straight-hole motors were used in the intermediate sections for rate of build advantages and to keep the hole straight. Curves were built with either 1.8 or 2.3 bend motors to approximately 60 to 70 degrees before setting pipe.
The next step was to trip in hole with a rotary steerable system (RSS) assembly and soft land the curve to 90 degrees, then drill the lateral, usually all in one bit run. A seven-blade PDC bit was used in the curve, and a long-gage, six-blade PDC bit was used with the RSS assembly to drill the lateral.
In the fifth well, the AFP 1H, a change was made in the well design, to kick off and drill the entire curve using an RSS, marking a first for this drilling methodology in the area. The objective of the change in well design was to lower overall well cost by using a deeper surface casing and eliminating the intermediate casing. The compromise involved uncertainty regarding achievable build rates. It was assumed that build rates with the RSS would not be as high as with a mud motor. What was not certain was the degree of build rate achievable with the RSS. Additionally, although it was known that build rates would increase with hole inclination, it was not known how much they would increase.
The well plan for the AFP 1H called for drilling from zero to 20 degrees of inclination at a four-degree build rate, then drilling from 20 to 90 degrees of inclination at a six-degree build rate. The curve was landed successfully on target, and lateral drilling continued to total depth.
Approximately 47 hours of drilling time were required to drill from zero to 90 degrees. The gun-barrel hole created by using the RSS made casing running simpler. The objective of eliminating a string of casing was achieved. An additional lesson learned from this well was that after reaching 40 degrees of inclination, the RSS could achieve larger doglegs (8 to 9 degrees/100 ft) consistently.
The PCQ 1 H, was the first Eagle Ford well to be drilled by Swift in McMullen County, Texas. This well was drilled with a pilot hole, which required an openhole whipstock. As a result, it would not be possible to kick off with an RSS.
The pilot hole was drilled to the target formation, cored, and logged. The kickoff point was determined, and according to the directional plan, a conventional directional assembly with mud motor was used to achieve a dogleg severity (DLS) of 8 degrees/100 ft (30 m). The plan called for the conventional assembly to drill to 30 degrees of inclination. However, a decision was made to pull the conventional assembly at 25 degrees of inclination and replace it with RSS.
The remainder of the curve and the lateral were drilled with a DLS of 6 degrees/100 ft with a single RSS bottomhole assembly (BHA) in a single run.
The PCQ 1H came online at 1,134 b/d of oil and 1.1 MMcf/d of gas. A total of 78 drilling hours was required for the curve, including the time taken to kick off from the whipstock with the conventional directional BHA. After the RSS was run in-hole at 25 degrees of inclination, an additional 55 hours was required to land the curve at 90 degrees. Drilling occurred at greater than 11,500 ft (3,505 m) vertical depth.
As Swift continued to appraise its large acreage position, two additional wells were drilled with pilot holes with similar rates of penetration, times, and build results.
Improving drilling efficiency
At this point in the drilling program, Swift and Weatherford began pursuing more aggressive techniques to increase DLS and reduce the footage required to land the curve.
The Hayes 1H was the first Eagle Ford well to be drilled without a pilot hole. Now, with three data points, the team was able to plan more aggressive DLS to land the curve. The plan called for DLS of 3 degrees/100 ft to 10 degrees of inclination, 4 degrees/100 ft to 40 degrees, 6 degrees/100 ft to 50 degrees, and 8 degrees/100 ft to 90 degrees.
The well was kicked off and the curve landed as planned, directly on target. This project also established a milestone as the first time Swift had successfully and consistently planned and built angle at 8 degrees/100 ft in the area using RSS. Drilling time from the kickoff point to the end of the build was 58 hours. Eliminating the whipstock had allowed for faster build rates to be achieved.
Aggressive RSS sets record drilling times
After landing the curve successfully in the Hayes 1H well, the drilling team decided to become more aggressive with DLS in curves in the next three wells. These were the AFP 2H, AFP 3H, and PCQ 4H. Currently, the team is building angle at DLS of 4 degrees/ 100 ft to 10 degrees of inclination, 6 degrees/100 ft to 40 degrees, and 8 degrees/100 ft to 90 degrees. One curve has been landed in 35 hours of drilling time.
The first of these, the AFP 2H, was drilled using RSS from the surface casing point at 5,800 ft (1,768 m) of casing. The RSS was used to drill out of the shoe track, and the well, including the casing point, curve, and lateral, was drilled to total depth (TD) in a single run. The total run was 9,421 ft (2,872 m).
A significant development in these wells was the completion of a joint project between Weatherford and Reed Hycalog to develop a long-gauge PDC bit to reduce vibrations on the RSS tool and increase RSS tool life. The AFP 2H well set a global record for Weatherford’s 63?4-in. RSS, and a global record for the long-gauge PDC bit. Based on these successes, Swift incorporated the new BHA into its Olmos/Eagle Ford drilling program.
In the second well, the PCQ 4H, the RSS again was used to drill up the casing shoe and reach TD in a single run. For this well, the total run was 10,792 ft (3,289 m), advancing the global record for the RSS tool, and for Swift, that had been set in the AFP 2H well. The team also reduced the vertical section footage required to land curve from approximately 1,000 to 775 ft (305 to 236 m).
The third well, the AFP 3H, also reached TD from the surface casing point in a single run. For this well, the total run was 9,569 ft (2,917 m), marking the second-longest run in the area and again breaking the record set the previous month by the AFP 2H well. The AFP 3H was drilled in 161?4 days.
At this point in the project, spud to TD time has been reduced from 40 to 16 days. The reduced drilling time has resulted in an overall per-well cost reduction of US $4.4 million and cut dry-hole cost to $1.8 million.
Swift has greatly reduced the time and cost to drill horizontal wells in its South Texas Eagle Ford and Olmos holdings, primarily as a result of improved well design that eliminated the intermediate casing string, and the aggressive use of RSS to drill from surface casing to TD in one run. Additionally, the operator believes that the gun-barrel holes resulting from using RSS rather than a conventional directional assembly are a major contributor to the success in running casing to bottom consistently.
Although 16 days to drill a well is fast, other operators in the area are drilling well depths at the same speed. However, Swift believes that it is the only operator in the area that is setting conductor casing.
Furthermore, it believes that the 400-ft (121-m) string of conductor set by the drilling rig provides an improved shoe integrity in the event of drilling through shallow gas that is sometimes encountered in the Eagle Ford and Olmos formations.
Going forward, as Swift gains data points, the drilling team is pursuing an even more aggressive plan for the operator’s Olmos wells. However,
the team plans not to raise its level of drilling aggressiveness in the
Eagle Ford. The difference in strategy derives from the fact that, to reach the Eagle Ford formation, it is necessary to drill through the Austin Chalk. That formation presents occasional difficulty in achieving planned DLS.