Surveillance Field Trial to Identify Thief Zones in MFF-09B, a well with a Controlled Acid Jetting (CAJ) Liner

Abstract

The Controlled Acid Jetting (CAJ) well design was developed by Maersk Oil for the development of relatively thin but aerially very extensive oil accumulations in low-permeability Chalk formations in the North Sea. These relatively low-cost long horizontal wells (up to 30,000 ft Total Depth) enabled the development of the Dan West Flank and Halfdan oil fields, which would otherwise have been uneconomic. Building on the favourable experience from the North Sea, Maersk Oil has also applied CAJ wells for the cost-effective development of the Al Shaheen oil field in Qatar. The initial development decision for CAJ wells to develop these waterflooded oil fields has effectively resulted in a zero (below Coil Tubing reach) well intervention policy in terms of inflow/outflow profile surveillance and subsequent treatment of any thief zones and/or high-skin intervals encountered. The initial field developments have met expectations with respect to development costs and initial oil production rates. A significant number of waterflood patterns now show faster than forecasted watercut development, which indicates the presence of non-conformances (i.e. natural and/or induced fractures acting as thief zones). When thief zones are present in water floods, oil ultimate recovery is lower than forecasted, which has triggered the need to develop new CAJ well intervention technologies for inflow/outflow profile surveillance and subsequent treatment of thief zones. A dedicated Long Wells Conformance Control (LWCC) team was set up in 2010 to accelerate the development and implementation of such new technologies for the North Sea and Qatar oil fields.