Abstract

This paper describe horizontal well CT acidizing design, valid practices and evaluation with good results. The Ahdeb Oil Field consists of sour, heterogeneous carbonate reservoirs with medium porosity (22 - 26%) and low permeability (5 - 20 mD), buried at depth of 2650 to 3150 meters, containing 0.2 - 3.5 mol% H2S and 3.0 - 4.5 mol% CO2, the degree of mineralization of stratum water being as high as 130,000 - 209,000 ppm, producing heavy oil with 22.5—28.9º API.

With very heterogeneous long section (24000ft-32000ft) open to flow, the acid placement and subsequent wormhole penetration depths are challenges. Integrated completion & stimulation techniques have an increasingly wide utilization in Ahdeb Oil Field. Such as: Using of Oil Swell-able Packer for completion of horizontal wells. The strategies related to the acidizing design included various velocity withdrawing pin-point acid jetting and acid. CT is withdrawn continuously from high to low velocity along the whole horizontal section. Viscoelastic acid treatments help to equalize acid distribution by special acid/rock reaction characteristic for each interval. The jetting action helps to remove deep damaged caused by the drilling fluid and completion fluid and improve acid penetration for relative low permeability section. The acidizing simulator predicts the distribution and penetration of acid during the acid treatment. N2 + CT techniques was used to clear up spend acid quickly.

In the past 3 years, there were over 59 horizontal wells that were stimulated with viscoelastic diversion acidizing using CT conducted achieving an averagely doubled production rate which was great contribute to the Ahdeb Oil Field with 120 mbopd of production capability. Besides, a modified evaluation model for horizontal well performance that can be used for field evaluation of acid treatments is developed based on treatment data. Skin factors performance as functions of position and time were calculated and analyzed for stimulated wells.

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