A Sweet Spots Prediction Method of Tight Carbonate Reservoir and Its Application in Horizontal Well Design

Abstract

Abstract Tight carbonate reservoirs are widely developed in Arabian Sea. The character of the reservoir indicates high heterogeneity, poor reservoir physical property and low productivity of which would lead to high Unit Technical Cost (UTC). Past drilling experiences show that thin sweet reservoirs identification is very important for field development. In this study, a new method of sweet spots prediction in tight carbonate reservoirs is carried out, and successfully used in horizontal wells design. Two main aspects of sweet spot reservoir were summarized based on this study: 1) For reservoir property prediction, multidisciplinary comprehensive research is used in this study. Seismic attributes fusion between amplitude and frequency is a main technical progress to predict the favorable reservoir. Where after, the porosity model is built by the constraint of fusion attribute and logging interpretation. 2) In terms of fluid mobility, rock type based permeability model is done to classify the flow capacity of reservoir fluid. The high permeability belt can be determined. Finally, integrate research will provide the evaluation map of sweet spots, then by which the horizontal trajectory is carried out. The study results show that sweet spots are those reservoirs with relative high porosity and high permeability compared to wall rock. Frequency and amplitude based seismic attributes fusion is a most effective way to characterize the favorable area in tight reservoir. In fluid mobility study, permeability model that constraint by lithological classification is very important to definite each flow unit of the sweet spots. Integrated analysis reveal that the sweet spots distribute in an overlap mode with poor connectivity between each reservoirs and the single reservoir thickness is only about 10~15m with an average porosity range 5%~15% and permeability range 0.1mD to 1mD. Based on the sweet spots characterization results, the horizontal well trajectory is designed to realize multi-reservoirs penetration. It is one of the best ways to maximum the well productivity, reduce the drilling risk and UTC. This study provide a new manner to predict sweet spots for tight carbonate reservoir and improve the success of horizontal drilling. The study results had been used in pilot well design in B oilfield, Abu Dhabi Offshore. The successful drilling experience can be used in the similar reservoirs of Middle East.