A Novel Hybrid Acid Stimulation/Fracturing Technique Developed for North Kuwait Jurassic Gas, Utilizing Particulate Diverters for Wellbore Diversion

Abstract

The North Kuwait Jurassic Gas (NKJG) asset is highly complex. The main target zone is the dolomitic Marrat reservoirs that have been under differential depletion and production for several years. The Marrat are deep carbonates, naturally fractured with low matrix permeability and high conductivity contrasts. Reservoir fluid composition is sour gas condensate and volatile oil mix supported by a weak water primary drive mechanism. The Marrat reservoir is divided into flow units/flow zones with variations in reservoir properties. The variations in properties, conductivity contrasts, and the propensity to flow preferentially from the naturally fractured network cause effective stimulation of individual flow zones critical for productivity enhancement. Ideally, each flow zone must be stimulated separately to optimize the productivity of the well and to prevent unintended bypassing of the Jurassic hydrocarbons. A customized deployment method that is neither fracturing nor matrix stimulation along with a temporary plugging mechanism is required to ensure high-rate matrix acidizing (HRMA) treatments will stimulate multiple flow zones with conductivity differences that are greater than an order of magnitude. The alternative plug-perforate-stimulate-repeat process has been successfully implemented, but it incurs much higher costs than conventional methods and requires a high demand of well intervention operational resources. Placement control is obtained by perforating each flow zone separately and then stimulating prior to isolating with a millable mechanical isolation plug. All the plugs are milled out, and zones are cleaned out to contribute to the overall inflow. The key driving force for using the plug-perforate-stimulate method in a multizone well is the effectiveness of the stimulation in treating each zone individually. Other means of placement, such as coiled-tubing-deployed stimulations, are less frequently utilized due to the cost and limitations in pump rate and pump pressure through the coil. Degradable particulate diverters were adopted as a cost-effective diversion technique that retained much of the advantage of a pinpointed or focused stimulation. The asset team worked closely with the service providers to determine the size, type, and volume of degradable particulate diverter pill to be deployed. Fracturing rates and pressures were determined prior to each treatment to ensure an HRMA treatment could be designed and deployed effectively to pump the stimulation fluid train at as high rate as possible to create wellbore diversion while not fracturing any of the combination of the flow zones. This paper summarizes the latest optimization and successful placement cases from a multiwell project where the wellbore diverters were optimized and placed in HRMAs and acid fracturing treatments where the results significantly exceeded expectations. Technical details of the actual cases are disclosed, and the latest developments are presented with actual field data.