Evaluation of Super-K Wells Performance Using Fluid Flow Index in Ghawar Field

Abstract

Abstract Reservoir management engineers at Aramco are fortunate to have a wealth of information about their reservoirs in the corporate database. However, this wealth of information comes with a challenge of analyzing this immense collection of data and utilizing this information for decision-making. In this study we used data mining process to explore our database and evaluate the performance of wells in a study area of Ghawar field. The performance of more than 450 wells was then related to the super-k existence from flowmeter data. The existence of super-k layer was believed to cause premature water breakthrough and hence poor vertical sweep. The objective of the study was to answer the following question: Will producing a super-k well without isolating the super-k layer result in less cumulative oil production after water breakthrough? In this paper we developed a methodology to identify and quantify super-k while avoiding the pitfall of black or white (i.e. super-k or non super-k well). Super-k quantification was accomplished by deriving Fluid Flow Index from flowmeter surveys. The next challenge was to come up with a consistence measure of well performance so that all the wells can be compared on the same basis. This challenge was overcome by introducing the new definition of cumulative oil production and average oil rate after water breakthrough. In this paper we developed correlations to predict the performance of future wells to be drilled in the area. The study indicated that there was a positive correlation between super-k and high average rate after water breakthrough. Also, it was found that anomalous flood front encroachment in the east flank of the field is unrelated to the super-k. The study showed that reservoir performance is controlled by the interaction between Faults/ Fractures and Super-k layers. The results of this study created a paradigm shift in perceiving super-k layers in Ghawar. Field data showed an improved well performance by perforating isolated super-k layers. Moreover, the derived Fluid Flow index was used in building an enhanced and more realistic model for the field. Introduction Super-K or extremely permeable intervals are quite common in the study area of Ghawar field. In this carbonate reservoir, super-k zones can be horizontal layers, created during deposition or after digenesis, or they are just as likely to be sub-vertical fractures and faults1. However, since most of the wells in the study area are vertical, the probability of intersecting sub-vertical fractures and faults is very low. The first approach to treating super-k zones in carbonate reservoirs is to identify the nature of these zones in the wellbore. To this end, flowmeter logs is required to first identify potential zones and second characterize their properties. Continuous flow meters are routinely obtained in wells with openhole completions in Ghawar field to improve sweep from all the zones. It became apparent that in some wells, extremely high fluid-flow was confined to thin, apparently strati-bound ‘super-permeable’ intervals. This is in marked contrast with other wells, where continuous flow meters indicated that the fluid flow was distributed more uniformly across the openhole reservoir section.