Abstract

Marrat reservoir in Magwa field in Greater Burgan, Kuwait is a carbonate heterogeneous reservoir belonging to Lower Jurassic. Marrat is classified as a tight reservoir with an average permeability of 17md and contains light oil of 38deg API. The formation is around 2400ft thick divided in three sub layers namely Upper, Middle and Lower Marrat. Middle Marrat is the main oil reservoir which has been perforated and tested to be oil producing in almost all the 30 drilled wells. The reservoir consists of Grainstones, Packstones, Wackstones and Mudstones. Marrat was put on production in 1984 and solution gas drive is the main drive mechanism. The reservoir is naturally depleted due to limited water aquifer. The reservoir pressure declined 17% from the initial reservoir pressure within 15 years to current pressure of around 8000 PSI. Field Development Plan envisages pattern and peripheral water injection and facilities development for water injection is planned. Asphaltene flocculation at wellbore, tubular and surface facilities has been recognized as a severe problem. One of the options to avoid asphaltene problems in the reservoir, including the near wellbore region, is to maintain reservoir pressure and flowing BHPs above the asphaltene onset pressure (AOP) of ~ 6500 PSI.

Formation fluid contains around 1000 ppm of H2S and 4% CO2 which throws a corrosive environment also to tackle with. The well head equipment with present metallurgy often leaks on pressure tests and there is a plan to replace during future work over jobs. Coil Tubing Cleaning of tubular with light aromatics is a routine operation to maintain production from wells.

Increased demand of oil necessitated safely increasing oil production from Marrat reservoir. Keeping in view the challenges, a multi-disciplinary team was formulated to look into all possibilities. Focus was on Acid Fracturing Technique which had proved to be successful in the past. However with advancement in acidizing and diversion chemicals, the new system was field trialed.

This paper will discuss the process to select the wells and successful attempt of acid fracturing in two wells to tap oil from new areas.

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