SAGD as Follow-Up to Cyclic Steam Stimulation in a Medium Deep and Extraheavy-Oil Reservoir

Abstract

Guan-tao oil layer of Shu 1 Block in Liaohe oilfield is a medium deep and extra heavy oil reservoir, which has high porosity and high perm with edge water. In 2001, cyclic steam stimulation was applied with square well pattern and well-space 70m. After 9–10 cycles the stimulation development effect deteriorated and the degree of reserve recovery was only about 15%. To seek development method of extra heavy oil reservoir and improve the entirety recovery ratio of this block, after the feasibility research on SAGD technology in Guan-tao oil layer was finished, horizontal wells were infilled between vertical wells and 4 SAGD pilot test well groups combining vertical wells with horizontal wells were conducted Three cycles of cyclic steam stimulation to preheat the formation and decrease pressure were proceeded and the 4 well groups had produced for 1 year after converted to SAGD. Daily oil production capacity of single horizontal well increased from the initial 20–40t/d to 70–80 t/d after the multiple adjustment of the injection-production parameters. Preferable period effect was accomplished and the test provides good guide for same medium deep and extra heavy oil reservoir to change their development methods. Survey of the test block Block Du 84 locates on the middle of Huan-Shu structural belt of the western slope in the West Depression of Liaohe Basin. The Guan-tao oil-layer of Block Du 84 , shallowly buried , is a thick blocklike extra heavy oil reservoir with high porosity , high perm to extra high perm and , underscreen water??basal ground water and edge water. SAGD pilot test area lies in the north of Block Du 84(Figure 1). It is a monoclinal structure acclive to south-east and the structural dip is about 2–3 degree. No fault is found and its sands distribute continuously. The oil layer depth is 524–668m and the average net pay thickness is 91.7m, no basal ground water is found. The reservoir lithology was chiefly middle-coarse sandstone and inequigranular sandstone, average median grain diameter is 0.42mm. Reservoir quality is good , the average porosity is 36.3% and average perm is 5.54µm2, average oil density under 20°C is 1.007 g/cm3, the degassed oil viscosity under 50°C is 23.191×104 mPa·s, resin and asphaltine is 52.9%, solidifying point is 27°C, paraffin content is 2.44%, the oil-bearing area is 0.15km2, geologic reserve is 249×104t, and the initial formation pressure is 6.02MPa. Progress of the test Based on the development condition and well pattern of extra heavy oil reservoir in Block Shu 1, and associating with the result of numerical simulation, SAGD pilot testing program concerning vertical and horizontal wells was drawn up. Four infilled horizontal wells named Guan-ping 10-- Guan-ping 13 were selected to form test well groups with around 34 vertical wells. The injector-producer distance is 35m, horizontal well spacing is 70m, horizontal segment size is 350–400m. What differs from in Canada is that the producing horizontal wells were infilled between the used vertical wells and below the vertical wells, 5m distance from the perforated intervals of vertical wells. The test from December of 2003 to June of 2006 was devided into two periods: steam huff and puff period to preheat the formation, SAGD producing period. Cyclic steam stimulation period to preheat the formation The pilot test block is a medium deep reservoir and the initial formation pressure is comparatively high. CSS has been applied in vertical wells for average 7.2 cycles before participate in preheat together and the recovery percentage was 12.7%. However, the formation pressure between wells didn't fall down too much. Because the horizontal wells are allocated between vertical wells where thermal connect doesn't exist and operation should be under low pressure condition during SAGD period, vertical wells and horizontal wells operate together during cyclic steam stimulation period to preheat the formation to achieve the condition help to convert to SAGD.

A Critical Review of Reservoir Simulation Applications in Key Thermal Recovery Processes: Lessons, Opportunities, and Challenges

“…SAGD pilot tests have been applied in Canada, China, United States, and Veneruzla, but it had the biggest commercial success in McMurry formation, Athabasca, Canada, including Hangingstone, Foster Creek, Christina Lake, and Firebag . In Canada, this successful application was extended to Clear Water Formation in the Cold Lake and Lloydminster areas .…”