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A Study on Increasing the Number of Stages in the Acid Fracturing Stimulation Technique in Horizontal Wells for a Tight Fractured Carbonate Reservoir in the Bahrain Field


 The Ahmadi formation of Bahrain field is of Middle Cretaceous age. It is predominantly a shale lying immediately below the Magwa member of the Rumaila formation and contains two limestone units in the Bahrain field, which are referred to as Aa and Ab members. Limestone Aa and Ab are present with practically uniform thickness over the entire Bahrain field area, as a blanket like deposition.
 The Ahmadi Reservoir in the Bahrain Field has been producing since 1933. Ahmadi consists of two main limestone units, AA and AB, separated by a 40-45 ft shale member. The AA reservoir is typically 3 to 4 feet thick, while the AB is divided into three separate units: AB1, AB2, and AB3. AB1 and AB3 are fairly clean limestone units, with a cumulative net reservoir of 12 to 14 ft. AB2 is about 4 to 5 feet thick, and characterized as a non-reservoir. The matrix permeability ranges from 1 to 2 mD.
 The main focus of the primary development plan was established by infill horizontal open hole lateral section, targeting the AB3 zone. However, poor matrix permeability and the irregularly spaced natural fracture network of the AB3 zone can hinder the primary development strategy and well production. Therefore, acid fracturing with 8 stages (60 ft each) in the open hole lateral section was implemented to improve well performance.
 A study was initiated in 2019 to improve the acid fracturing technique in the AB3 open hole lateral section (horizontal wells) by increasing the number of stages from 8 stages (60 ft each) to 18 stages (60 ft each). The wells targeted were located in areas with low reservoir quality and low fracture networks in order to induce artificial fractures, thereby improving well performance.