Engineering and Operational Issues Associated with Commingled Drill Cuttings and Produced Water Re-injection Schemes

Abstract

Current BP Group Environmental Expectations of zero discharge of oilfield waste to the environment by 2005 and reduction in land-fill disposal options are driving the Company towards innovative disposal schemes that offer attractive and significant environmental and operational cost benefits. One of the current BP initiatives is to merge the synergies of both produced water and drilling cuttings into a single commingled re-injection scheme in the same well. Merging the two technologies for waste disposal in the same formation in the same well becomes a very attractive option, if the well can be engineered and completed to meet the specific objectives of disposing of large volumes of produced water and periodic disposal of drill cuttings from in-fill wells. The main advantages of such a disposal scheme are: Better assurance of fracture containment for disposal of oil-contaminated cuttings.; Reduced cost of both operations because of fewer wells and reduced chemicals cost than would be required for separate drill cuttings and produced water disposal schemes.; Potential recovery of disposal cost with secondary recovery, if suitable targets are available. BP has successfully implemented commingled re-injection of produced water and drill cuttings in the Wytch Farm and Valhall fields. These commingled re-injection schemes were implemented to address urgent operational need to manage drill cuttings disposal when only water injection wells or producers were available. This paper addresses key engineering issues and risks, which are being evaluated as part of an ongoing BP project to develop engineering guidelines for commingled produced water (PWRI) and drill cuttings (DCRI) re-injection. The paper outlines synergies and differences in current DCRI and PWRI processes and the dominant parameters that are likely to control successful commingled re-injection process.