Methods of Isolation and Diversion for High Rate Carbonate Acidizing

摘要

Some form of acid treatment is generally required when completing wells in carbonate reservoirs. The treatment objectives range from near well damage removal to true stimulation, using well work techniques that range from acid washes to acid fracturing. All depend on delivering the appropriate acid volumes to the right intervals at the rates needed to achieve the desired results. Because most carbonate reservoirs feature multiple layers, implementation often requires a combination of isolation - separating a particular zone so it alone receives treatment - and diversion, directing the acid from zone to zone as the treatment progresses. Conventional elements of the acidizing toolkit include mechanical plugs, limited entry perforating, ball sealers, and a variety of chemical and particulate diverting agents. In long deviated completion intervals, a multi-stage perforation / stimulation approach was previously developed and implemented. Successful stimulation and resulting productivity of all target intervals was achieved through a combination of selective perforating, high-rate acid injection, fluid diversion, and linking stimulation results to long-term performance. However, in wells with existing perforations, this approach is not possible. Use of high rate and diverter fluids alone may not provide sufficient diversion to achieve the desired stimulation effectiveness. This paper describes the initial development of an innovative destructible ceramic plug and seat system as an alternative option for diversion or acid placement during multizone acid treatment. The plug would enable acid diversion in multizone reservoirs with large pressure differentials and/or permeability contrast between the zones. The design and testing of the plug system included Finite Element Analysis (FEA) modeling of the plug, manufacturing of the plug and seat, mechanical strength testing and destruction testing.