Development of the Alba Field-Evolution of Completion Practices, Part 2: Openhole Completions, Conventional Gravel Packing After Drilling With SOBM
- G. Murray (ChevronTexaco) | K. Morton (ChevronTexaco) | S. Blattel (Halliburton Energy Services Inc. Baroid) | E. Davidson (Halliburton Energy Services Inc. Baroid) | N. McMillan (Halliburton Energy Services Inc. Baroid) | J. Roberts (Halliburton Energy Services Inc. Baroid)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- December 2003
- Document Type
- Journal Paper
- 311 - 317
- 2003. Society of Petroleum Engineers
- 3.3.1 Production Logging, 1.6.9 Coring, Fishing, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 2 Well Completion, 1.14 Casing and Cementing, 2.7.1 Completion Fluids, 1.6.10 Running and Setting Casing, 1.10 Drilling Equipment, 2.2.2 Perforating, 1.11 Drilling Fluids and Materials, 2.4.3 Sand/Solids Control, 1.8 Formation Damage, 4.1.5 Processing Equipment, 3.2.5 Produced Sand / Solids Management and Control, 1.6 Drilling Operations, 2.4.5 Gravel pack design & evaluation, 4.1.2 Separation and Treating
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Chevron has been successfully drilling and gravel packing openhole horizontal wells in the Alba field (central North Sea) since 1998, and 13 openhole gravel-packed (OHGP) wells drilled with water-based mud (WBM) are currently in production with no history of sand production. Although these wells have been hugely successful with significant net present value (NPV) returns, it was recognized that the future, mature redrill and infill targets cannot sustain the current costs associated with traditional OHGP completions. The challenge was to develop alternative techniques to maintain the benefits of OHGP wells but to achieve a low-cost well and completion concept to assist in realizing new drilling opportunities.
Drilling the shale above the top of the reservoir and the productive interval in a single hole section would require removing conventional requirements for setting an additional casing string and changing over to a water-based system before drilling into the reservoir. This would save costs but raises a question concerning the gravel-packing operation. Hitherto, attempts to gravel pack that involve alpha/beta placement techniques using an aqueous carrier fluid following drilling with oil-based systems have had only limited success.
The prospective problems were examined by extensive laboratory tests carried out cooperatively by Baroid and Chevron. A new, synthetic oil-based mud (SOBM) formulation was developed, and compatible displacement fluids and procedures were devised.
Based on this work, 1,500 ft of shale and reservoir were drilled, a liner that was predrilled over the reservoir section was installed, and screen was run inside the liner. Gravel was pumped using brine as the carrier fluid, and complete gravel placement was achieved. The well has achieved productivity levels at least as good as existing WBM wells. A second well completed in the same manner has given a similar performance.
This combination of a liner system and SOBM fluids offers several advantages. There is the prospect of considerable savings with respect to operating time, cementing, and drilling fluids. The liner also gives protection to the screen.
This new approach, which represents potential large savings in costs and excellent productivity, is considered applicable to other types of completions when it is desirable to drill with oil-based mud even though conventional thinking would have called for water-based drill-in fluid. This consideration applies to targets in the Alba field and worldwide.
The Alba oil field, located in Block 16/26 of the U.K. sector of the North Sea, comprises an Eocene sandstone formation that is thin; highly porous and permeable; very unconsolidated; and overlain by a bed of impermeable, highly reactive shale. The nature of the reservoir dictated that development would be best achieved by openhole completions and highly deviated or horizontal reservoir sections with the productive interval located near the top of the sand body. The earliest approach was to run screen-only completions, with SOBM as the drill-in fluid. The next stage of the evolutionary approach involved the same screen arrangements but with a saturated brine/sized sodium chloride-based drill-in fluid. Both approaches provided excellent drilling properties, but there were severe limitations with respect to productivity for the wells drilled with SOBM, and screen longevity was a problem for wells using the sized-salt approach.1 Both issues were addressed by adopting a sized carbonate drill-in fluid and performing openhole gravel packs on the productive sections. From 19981 to July 2001, 13 openhole sections had been successfully gravel packed and are still in production with high flow rates and no history of sand production.
However, it was recognized that despite the excellent flow rates and significant NPV returns provided by these wells, the future mature redrill and infill targets could not sustain the current costs associated with traditional OHGP completions. The asset was challenged with developing alternative completion techniques to maintain the benefits of OHGP wells while reducing the costs of current drilling and completion procedures and developing a low-cost well concept to assist in realizing new drilling opportunities.
The ability to gravel pack openhole sections drilled with SOBM would enable the shale above the top of the reservoir and the productive interval to be drilled in a single hole section. This would remove the requirement to install an additional casing string and to change over to a different mud system before drilling into the reservoir. For example, in the case of a redrill in Alba W33, there was the prospect of saving a casing run of more than 1,000 ft and using one mud system throughout. Potential total savings with respect to operational time, cementing, and drilling fluids were estimated to be of the order of U.S. $3 million.
On the other hand, experience with completions in the Alba field (with the interval drilled with SOBM and the completion fluid as brine) has not been encouraging. During the early stages of the Alba development, several productive intervals were drilled with SOBM and displaced to aqueous completion fluid; the productivity of the wells was much less than expected.1
The gravel-packing technique used in Alba for the previous wells drilled with water-based drill-in fluid involved the alpha/beta wave-placement method. It was intended that the same method be used for the wells drilled with SOBM. As a result, significant fluid loss during gravel placement would not be tolerable. Indeed, previous attempts to drill with SOBM and gravel pack with aqueous carrier fluid in the manner envisaged for Alba have reported limited success,3* mainly because of problems caused by excessive fluid loss. Similarly, a development in west Africa involving drilling with oil followed by an aqueous, gelled, gravel carrier fluid reported losses on two of the three operations.4
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