Increasing Recovery in the Complex Reservoirs in the Al Shaheen Field, Offshore Qatar, by Mastering Reservoir Pressure for Large Scale Horizontal Infill Drilling

摘要

The giant Al Shaheen field offshore Qatar comprises six stacked carbonate and sandstone reservoirs developed with extended reach horizontal wells. More than 130 horizontal production and injection development wells had been drilled up to end 2005 when implementation of a new large scale field development plan commenced. The new development plan, FDP 2005, comprises 163 additional horizontal development wells from six existing and three new locations. The initial development phases in Al Shaheen comprised radial and parallel well patterns of long horizontal wells with a well spacing designed to enable effective appraisal and data gathering. A significant part of the FDP 2005 is dependent on successful horizontal infill drilling where close well spacing is required to ensure optimal recovery of the low permeability carbonate formations. The combination of stacked reservoirs, reservoir heterogeneities, long horizontal wells, close well spacing and past production and injection result in pressure regimes along the wells which are challenging to predict but crucial to manage for successful well planning and execution. Successful implementation of the FDP 2005 requires a detailed and systematic approach for reservoir pressure conditioning to ensure acceptable pressure gradients along the new wells while at the same time minimize the impact on the short term oil production. This paper describes the challenges related to the reservoir pressure conditioning in the complex Al Shaheen field offshore Qatar. The applied methodology covering systematic use of reservoir simulation models, nodal analyses, pressure transient analyses and timely shut-in of producers and injectors to map and manage pressure regimes is presented.