Effluent Water Disposal Experiences in the Greater Burgan Field of Kuwait

Abstract

Abstract This paper presents the process of candidate well selection, design, execution and evaluation that lead to the successful implementation of acid fracturing treatment in Marrat field. The acid fracturing treatment is quite challenging due to presence of high pressure/high temperature and high asphaltene content in the crude oil which renders the situation even more difficult because of fluid incompatibility issues. The formation tends to produce oil with asphaltene content when the flowing bottomhole pressure is drawn below the Asphalting Onset Pressure (AOP). An engineering solution was urgently needed to enhance the productivity of wells and to mitigate the aspheltene deposition issue by allowing the wells to produce above the AOP. The option of acid fracturing was evaluated and found to be feasible to alleviate the problems. The paper details an optimization workflow and integrated evaluation process that improve the treatment performance. Detailed fluid system used in the treatment is discussed in details including the application of polymer-free viscoelastic surfactant based fluids. Also, a surveillance program was implemented to monitor and evaluate the acid treatment. It is anticipated that the matured giant reservoirs of Southeast Kuwait are going to produce substantial amount of water in future during EOR process. The Greater Burgan field is currently producing about 250,000 barrels of effluent water per day. Kuwait Oil Company has the mandate to achieve the target of subsurface disposal of all produced water and zero discharge to the environment. In long term, several enhanced recovery projects would be implemented and the produced water would be reinjected to the producing reservoirs for pressure maintenance schemes. The shorter term need is to dispose of the water into selected non-producing reservoirs. Several non-producing reservoirs were evaluated. The Burgan Fourth Sand, which is mainly below the oil water contact in most part of the field, was identified as the target disposal reservoir in view of its large capacity and connection with the aquifer supporting the field. Disposal well was drilled and closely monitored. Early attempt to inject untreated effluent water in this well encountered frequent increase in the wellhead pressures. Acid jobs were carried out to restore injectivity. Laboratory studies confirmed the reasons of plugging as water incompatibility and made several recommendations for maintaining water quality. Two effluent water treating plants have since been built based on these recommendations. Along with water specification team, an earth scientist team has studied alternate option of finding a carbonate reservoir that can handle the existing water specification. An existing well was made deepened to Shuaiba carbonate reservoir. The key to a successful injection in this formation was thought to be our ability to intersect the fracture network. Special drilling and completion techniques were used to extend the well horizontally into the Shuaiba. It's been two years of injecting the untreated water to this reservoir without any major problem in term of plugging. From the experience of injecting in Shuaiba, it is apparent that the formation is very forgiving in term of effluent water quality. However, it is not known how long the Shuaiba can take the untreated effluent water due to its smaller storage capacity and uncertainty about connectivity with overlying reservoirs. Therefore, the current strategy is to combine the two options and to continue focusing on water treating prior to disposal to meet water quality specifications and applying the proper chemicals to control scaling and corrosion. The Fourth Sand will remain as a back-up in case the Shuaiba is filled up sooner than anticipated. The paper discusses the issues associated water injection in to clastic and carbonate reservoirs and the strategy in detail. Introduction Burgan Field, the world's largest sandstone oil field, lies 35 km south of Kuwait City near Ahmadi, Kuwait. The four main reservoir units comprising the Greater Burgan Field complex are the Wara, Mauddud, Burgan Third Sand and Burgan Fourth Sand. Additionally, there are several smaller and deeper hydrocarbon reservoirs such as the Minagish and Marrat which has limited production. In between the main reservoir and the deeper reservoir lies the Shuaiba, this is a non hydrocarbon bearing carbonate reservoir (Fig.1).