Pressure Gradient Testing With a New Formation Pressure Testing During Drilling Tool

Abstract

Abstract Formation pore pressure is a key parameter for reservoir management in the Troll field. The pressure measurement traditionally performed on wireline is time consuming, especially in deviated wells. To provide the service earlier and more efficiently, a formation pressure tester has been developed as part of a Logging While Drilling bottom hole assembly. The tool measures pore pressures during brief pauses of the drilling process by extending a pad to the borehole wall, forming a seal against the formation, and performing a series of drawdowns. To meet the challenges of short station duration and limited telemetry rates, the new tool is equipped with a downhole intelligent system for real-time operational decision. The flexibility of the design of the new tool allows basic pressure tests with preset draw down and buildup tests with preset fixed volume and rate, or repeated draw down and buildup tests with different drawdown rates and volumes optimized downhole in real-time. The new LWD formation pressure testing tool (TesTrak) has been successfully applied in three deviated wells with inclinations between 50 and 90 degrees in the Troll field. In eight bit runs and 235 rotational hours, 231 pressure points at 89 stations have been performed over a drilling distance of 10,780 ft. Post-well analyses of the pressure data have further added confidence to the real-time data acquired during drilling. The objective in the first field test was to establish the pressure in a high and a low mobility sandstone section on both sides of an intersecting fault zone. In addition, reservoir connectivity between two compartments was proven with the real-time data. The objective of the second field test was to establish a fluid gradient in the well during a small TVD change in the horizontal section. The tool provided a real-time fluid gradient in the reservoir section over a 20 feet TVD drop over a 1000 ft long section. The pressure data were also used to optimize the mud program and drill the well efficiently. In the third field test three pressure gradients (one gas, and two water gradients) were established, which helped to determine reservoir depletion characteristics. The tool performed well and subsequent analysis of memory data supported the real-time pressure measurements. The data obtained fit perfectly to the pre-drill model, which was based on wireline formation tester measurements in off-set wells. The successful operation of the LWD Formation Pressure Tester demonstrates a good potential for time/cost savings by replacing separate wireline- or pipe-conveyed formation pressure logging jobs. The pressure data could also be applied for optimizing the mud program and hence improve drilling efficiency. Introduction The Troll field (Figure 1) is one of the most important oil and gas producers in Norway. After discovery in 1985, development drilling using horizontal wells started in 1991. Improved horizontal drilling techniques with Rotary Steerable Systems allowed the drilling of long horizontal wells in the oil zone of the Troll West Gas province. Most wells nowadays are drilled as multilaterals.