Application of CSS to Develop a Thick Heavy Oil Field in South Oman

Abstract

Abstract The "A" East is a heavy oil reservoir in the south of Oman. It was discovered in 1978. The reservoir is sandstone with a 200m thick oil column. Oil sampled from the field showed high oil viscosity and was considered to be problematic for primary production. In 2008, the field development plan proposed to develop the field thermally, starting with cyclic steam stimulation and followed by steamflood. CSS trials (2008 – 2010) were carried out in three wells using temporary facilities to evaluate the injectivity and productivity of the wells. This helped to identify the surface and subsurface challenges in the field and resulted in modifications to the full-field CSS deployment. During the drilling campaign (2010-2012), a crestal well was cored and oil viscosity data was acquired. The results showed oil viscosity varies from 400 to 400,000 cp (at 55°C) from top to bottom of the reservoir. Production testing, using portable tanks proved the cold production concept. 32 out of 81 wells were selected to be initially cold produced by PCP before converting them later to CSS. On 9th March 2013 cold production from crestal wells started, which provided early production. One of the subsurface concerns identified during the "A" East field development study was the effect of the high initial reservoir pressure (~11,500kPa) on steam injection efficiency. Cold production helped to lower the reservoir pressure. Recently acquired pressure data indicate that the reservoir pressure fell to around 4000 kPa in the crestal area and to 6000 – 10500 kPa on the flanks of the accumulation. "A" East steam injection started on the 2nd of March 2014. Initial injection data suggest that higher injection rates were achieved due to the lower reservoir pressure from cold production. The current plan is to ramp up steam injection and increase the number of CSS wells through converting more of the cold production wells to CSS. CSS operations will then be followed by pattern type steamflood (inverted 9 spot) once the reservoir pressure is depleted and connectivity is established between the wells.