Al-Obaidli, Asmaa (KOC) | Al-Nasheet, Anwar (KOC) | Snasiri, Fatemah (KOC) | Al-Shammari, Obaid (KOC) | Al-Shammari, Asrar (KOC) | Sinha, Satyendra (KOC) | Amjad, Yaser Muhammad (Schlumberger) | Gonzalez, Doris (BP) | Gonzalez, Fabio (BP)
The Magwa-Marrat field started production early 1984 with an initial reservoir pressure of 9,600 psia Thirtysix (36) producer wells have been drilled until now. By 1999, when the field had accumulated 92 MMSTB of produced oil and the reservoir pressure had declined to 8000 psia, the field was shut-in until late 2003 due to concerns on asphaltene deposition in the reservoir that could cause irreversible damage and total recovery losses. The field was restarted in 2003 an it has been in production since then. By April 2018 the field had produced 220 MMSTBO, with the average reservoir pressure declined to 6,400 psia. As crude oil has been produced and the energy of the reservoir has depleted, the equilibrium of its fluid components has been disturbed and asphaltenes have precipitated out of the liquid phase and deposited in the production tubing. There is a concern that the reservoir will encounter asphaltene problems as the reservoir pressure drops further. The objective of this manuscript is to present the process to understand the reservoir fluids behavior as it relates to asphaltenes issues and develop a work frame to recognize and mitigate the risk of plugging the reservoir rock due to asphaltenes deposition with the end purpose of maximizing recovery while producing at the maximum field potential Data acquired during more than 30 years have been integrated and analyzed including 22 AOP measurements using gravimetric and solid detection system techniques, 17 PVT lab reports, 1 core-flooding study and 1 permeability/wettability study. Despite the wide range of AOP measured in different labs, it was possible to determine that the AOP for the Magwa-Marrat fluid is 5,600 500 psia and the saturation pressure is 3,200 200 psia. Results of this fluids review study indicates that it might be possible to deplete the reservoir pressure below the AOP while producing at high rates.
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.