Evolution of Coiled Tubing Matrix Stimulation for Gas Wells in Saudi Arabia

Abstract

Saudi Aramco has been using coiled tubing (CT) to acid stimulate gas wells completed as single or multiple open hole horizontal laterals in carbonate reservoirs. These CT interventions have evolved from pumping the treatment fluids through normal nozzles, to high-pressure jetting with or without a simultaneous bullheading of inert fluid through CT tubing annulus. Until recently, there was no CT bottom-hole assembly (BHA) available on the market to provide realtime downhole data monitoring during CT acid stimulation. Therefore, these types of stimulation jobs followed a predetermined pumping schedule, assuming that fluids are squeezed at the nozzles depth while reciprocating the CT string from toe to heel. The operator had no means to control the acid coverage across the extended reach open hole laterals.The bottom-hole pressure (BHP) inside and outside the CT string, monitored real-time with the fiber optic bottom-hole assembly (FOBHA) allows the operator to adjust the differential pressure across the high-pressure jetting tool nozzles. The distributed temperature survey (DTS) recorded with the fiber optic at key stages of the treatment helps identify initial thief zones and any further developing ones during the acid stimulation treatment. Tracking with a DTS, the fluids placement through the high-pressure jetting tool showed that acid was still being injected into thief zones and not squeezed at the nozzles depth. DTS is therefore used to adjust the real-time pumping schedule by deciding when, where, what type and what quantity of diverter to pump to get uniform acid placement across target intervals.The ability to place stimulation fluids in a highly effective way is the most important element in any successful production enhancement stimulation job. This paper will detail case histories of gas producers in which a fiber optic enabled coiled tubing (FOECT) and a FOBHA were successfully run together to record real-time downhole data in an effort to assess the full stimulation effect of an acid matrix stimulation treatment, and to control and optimize the CT operation.Several cases demonstrating the effectiveness of the FOECT matrix stimulation technique are highlighted in this paper.