Utilization of Biologically Generated Acid for Drilling Fluid Damage Removal and Uniform Acid Placement Across Long Formation Intervals

Abstract

Abstract A method of drilling damage removal is presented which uses biologically generated acid (BGA) as the stimulation fluid. The BGA solution is not reactive during the actual pumping stage which allows its displacement into the reservoir to be controlled by the relatively low permeability of the near wellbore damage. Catalytic generation of acid occurs at a controlled rate once the BGA has been injected into the formation and results in uniform damage removal around the near wellbore region. The ability of BGA to be generated under a variety of temperature and pressure conditions and the compatibility evaluation of BGA with a variety of commonly used oil and water based drilling muds is first presented to establish some of the operational guidelines for BGA use. Drilling damage removal studies utilizing the modified API linear conductivity flow cell and carbonate material with BGA is presented to demonstrate the effectiveness of this stimulation fluid. Dual core flow test data is then presented which shows BGA's ability and HCL's inability to remove drilling damage over long horizontal intervals in carbonate formations. Introduction The introduction of acid to remove formation damage was first introduced to the petroleum industry by Frasch in 1895. There have been significant improvements over the past few years in recognizing and describing the various types of formation damage, and many publications have appeared on the subject. Formation damage resulting from drilling, cementing, completion/workover, gravel pack, production, and stimulation operations have been reported and reviewed recently. The removal of drilling fluid damage across producing intervals of oil and gas wells is required for production optimization. In general, the damage is removed through injection of acid as a stimulation fluid. The most commonly used acid for drilling damage removal in carbonate reservoirs is hydrochloric acid. Hydrochloric acid (HCL) has been used with success in conjunction with a variety of diversion techniques and coiled tubing in wells with relatively short production intervals. However, the difficulty of applying HCL in extremely long horizontal producing intervals to uniformly remove drilling damage has been identified by several operators as a very serious problem with the result being disappointing well productivity. P. 465