Evaluation of Acid Treatment Results for Water Injection Wells in Saudi Arabia

Abstract

Several acid treatments were conducted in the Ghawar filed to increase the well injectivity and to support the reservoir pressure in this area. Vertical and horizontal wells with an open hole completion in a carbonate reservoir were selected to be a candidate for post acid treatments evaluation study. These wells were stimulated using hydrochloric and emulsified acid with foamed viscoelastic-based water. Viscoelastic-based water system was used to enhance the diversion mechanism and the lifting process for the spent acid following the treatment. In this paper new correlations for acid treatment design were obtained from an extensive study of several case histories that can be used for optimizing future acid treatments design in the Ghawar field. This study was mainly utilized the results from the post acid treatment jobs in terms of HCl acid, emulsified acid and viscoelastic volume correlated with the well's injectivity. Based on the study results, there is a strong relationship between the emulsified acid volumes with the injectivity index for the selected wells. Introduction The objective of matrix acidizing treatment is to remove or bypass formation damage by pumping the alternating acid stages into reservoir formation below fracturing pressure. In a carbonate matrix acidizing, an acid program is designed to create a wormhaoles that can produce a high permeability region radically around the wellbore leading in exceeding the natural permeability of the reservoir. Foamed viscoelstic based-acid system was used for first field application to obtain an efficient diversion process of Saudi Aramco field operation. 1 Viscoelastic surfactant fluid was used to improve the diversion process in acid stimulation treatment of water injectorwells.2 In addition, this chemical was successfully used to enhance the HCl viscosity during aicd placement in horizonlly oil wells.3 However, Polymer-based acids are not recommended to be used any more as a divertor in acidizing treatments for Saudi Aramco fields especially into low reservoir quality such as low permeability formation, due to residue effect which it might cause formation plugging. Therefore, vicoelastic surfact-based fluid is wildly used in acidizing a corabonte reservoir as a divertor fluid in both a producer and an injector wells when acid reacts with a formation leading to increase HCl viscosity solution and it can divert live acid into less permeable zones. Minimizing formation damage that occurs in power water injection wells is a critical point for increasing well potential and Injectivity index. In this paper, several types of chemicals were used in stimulation treatment such as plain acid, Diesel Emulsified Acid, foam and surfactant. Different volumes were pumped in each acid stimulation jobs based on the pay zone intervals. However, the volume of each chemical should be optimized to obtain high rate of succeed in acid stimulation results. In this paper, we applied a statistical study to obtain a correlation between volume of chemicals and Injectivity index at the same condition such as type of well completion, formation properties, and type of techniques that used in the job. Based on collected data, we obtained a good correlation between the Injectivity index and injected chemicals. Wells History Several wells were drilled as open hole water injector. The lithology of the reservoir is manly calcite with small volume of dolomite. Some of these wells weredrilledand completed as horizontal with open hole section length 1500 ft- 2800 ft and other wells weredrilledand completed as vertical with open hole section length 200 ft- 350 ft. These power water injection wells are located in Ghawar field.