Water Shut Off Techniques To Combat Premature Water Break Through In Mauddud Carbonate Reservoir - An Efficacy Analysis (2007)

Abstract Mauddud is a major hydrocarbon bearing formation in Sabiriyah field of North Kuwait. This carbonate reservoir is under depletion drive with no aquifer support and is currently producing under water flood with average water cut of 26 %. Water injection started in 2000 under 9-spot water flood pattern system and the water flood is maintaining a good pressure support in the reservoir close to initial reservoir pressure and well above bubble point pressure. However, the water production increased significantly due to premature water breakthrough, particularly in edge wells. This has led to an immediate need for implementing effective water shut off techniques for decreasing water production at the subsurface level to balance and better control the sweep of the reservoir. Consequently eight edge wells were identified after detailed studies of production history, PLT, water cut trend etc and taken up for water shut off jobs during the year 2005–06. Although in many of these wells, there were clear indications of water break through from bottom perforations, the option of plug back cementation could not be attempted for completion constraint as Mauddud was completed in short string of all the eight dual wells selected. The methodology adopted was cement squeeze followed by selective perforation keeping away from the possible high permeability "thief" zones based on the PLT analysis mainly. Every effort was made to ensure the integrity of the cement squeeze by conducting a positive pressure test followed by negative test during workover job. Utmost emphasis was given for a successful negative test @ 500 psi which is the representative operating draw down for Mauddud producers. Consequently squeeze jobs had to be repeated several times with special types of cements in certain cases, in pursuit of successful positive and negative tests and thereby accomplishing an effective squeeze job. The water shut off jobs on these wells had mixed success and an in depth analysis of pre-post job scenario on these wells is presented in this paper. Introduction: The Sabriyah structure is an elongated, north trending, faulted anticline with numerous grabens and associated relay ramps covered over an area of about 237 Sq. Km. The fault throws vary from less than 30 feet to more than 160 feet. The structural dip varies from up to 8 degrees on the eastern flank to 3–4 degrees on the western flank. The original oil/water contact is unknown and is most likely to vary by fault block. A schematic representation of field lithology is given in Fig1. Sabriyah field consists of three major reservoirs:MauddudUpper BurganLower Burgan Mauddud is a major reservoir of the filed characterized by a very stiff Limestone formation with low compressibility rock, inter-granular porosity, with very little or negligible development of secondary porosity. Eleven reservoir zones were identified in Mauddud and named from MaA to MaJ. The reservoir has a very weak and inactive aquifer. There was little to no need for water shut-off requirement felt in SA-Mauddud till the onset of water flood in 2000, and following few years, as most of the wells were producing water free oil. However as a result of ongoing waterflooding, the water production increased significantly and need was felt not only for enhancing water handling capacity at the surface, but also searching for sound techniques of decreasing water production at the subsurface level.