Integrated Reservoir Management in a Marginal Oil Rim Field

Abstract

Abstract The field under consideration is located about 50 Km offshore Nigeria in water depth of about 130ft. The field was discovered in 1968 with X1 well. This particular well encountered oil in four different zones (IX, X, XI and XII) in the Pliocene Agbada formation. The X1 well was logged and tested to evaluate the potential. The second well, X2 was drilled in the early 70s and that was in a separate fault block. This second well encountered oil in two reservoirs, IX and X. The XI was poorly developed in X2 well relative to X1 well which was found wet. The XII reservoir was encountered with good oil shows and gas readings were found in poorer sections of the reservoir. A third well was drilled which did not encounter any hydrocarbon and many of the sands were poorly developed or absent relative to the X1 and X2 wells. No testing was conducted in this well. The field was appraised with X4 well. The X4 well encountered oil in all the four sands. Pressure and log data were taken from the reservoirs in this well and the well was tested to know the true potential of each. The reservoir sands are of good to excellent quality but are unconsolidated and sand control will be required in the development phase. The fluid quality is 25 deg API with moderate viscosity and a moderate GOR in the XII, and about 14 deg API with high viscosity and low GOR in the other reservoirs. Reservoir pressure and temperature is normal in the IX sand, slightly over-pressured in the X sand and significantly over-pressured in the XII. Following the successful results of the subsequent appraisal programme, the reserves level increased significantly to more than 40 MMbbls. At this level the field was judged large enough to support a stand alone development. This had allowed a first proposal to initiate an initial development plan for the Field. Development drilling commenced in 2009 with first oil was recorded in 2010. As the development of the field progressed the lessons learnt from first development phase of drilling were implemented in the second phase. This led to better wells with improved production rates. In addition, effective reservoir management in the field has led to optimized production which saw recovery factor in these oil rim reservoirs getting above 30%. This paper highlights the challenges encountered, innovative solutions and key learnings along each phase of development.