An Integrated Evaluation of Successful Acid fracturing Treatment in a Deep Carbonate Reservoir having High Asphaltene Content in Burgan Field, Kuwait
Authors: Dashti Qasem M. , Kabir Mir Md Rezaul , Raju Vegesna , Al-Ruhaimani Feras Ahmad , Liu Hai 
Published: February 2016

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.

The first candidate well was fractured in June of 2006, achieving an increment of production from 2,798 BOPD to 5,353 BOPD maintaining the same wellhead pressure. The field results showed a significant improvement on post-fracture production and flowing pressure at both wellhead and bottomhole. A post-fracture pressure buildup test indicated a fracture linear flow with a fracture half length of 105 ft, high conductivity of 19,600 md-ft and an equivalent skin value of -5. The success accelerated the application of the treatment in other candidate wells chosen from the initial study.

Introduction

The Marrat reservoir in Magwa field of the Greater Burgan area has been producing since 1984 under a combination of rock and fluid expansion drive with low amount of reported water production. Lack of adequate aquifer support has caused field reservoir pressures to decline from an initial pressure of 9600 psia to the current average of about 8700 psia over a 15-year period.

The reservoir is under saturated and contains high quality light crude. However, production records show frequent asphaltene plugging problems in the production strings. Recent laboratory studies indicate a high asphaltene flocculation onset pressure of 6200 psia for the Magwa oil. This finding suggests the urgent need to implement an appropriate reservoir management strategy to conserve reservoir energy and to maintain the formation pressure much higher than the asphaltene onset pressure, to prevent asphaltene deposition within the reservoir in addition to accelerating oil recovery. One viable approach is to improve oil production. Improved oil production is required for Marrat wells to increase production and maintain the flowing bottomhole pressure above the AOP by reducing the pressure drop taking place in the formation particularly near wellbore. Production improvement can be achieved through the acid fracturing as it will be discussed in details in this paper. The planning and execution process of the acid fracturing treatment that was implemented is shown in Fig. 1. The detailed steps within this process are listed in Table 1.