Cross-flow to enhance gas recovery in the Dalton Field, East Irish Sea

Abstract

Dalton is a sub-sea gas field located in Block 110/2b of the UKCS in the East Irish Sea Basin. The field has been the subject of downward reserve revisions through its life based on increased geological understanding from well, production and simulation data. An innovative infill technique is proposed to reverse those trends and increase recovery by harnessing stranded reservoir gas. Dalton was discovered in 1990 by well 110/2b-9 which encountered a dry gas column of 345 ft within the Ormskirk Sandstone Formation of the Triassic Sherwood Sandstone. The field was developed in 1999 by wells 110/2b-R1 and 110/2b-R2. Wells were located on the eastern field crest in order to attain maximum gas column and maximize recovery from the good quality reservoir (average permeability >50mD). Production tests showed the majority of flow from the wells to come from thin, high permeability (>200mD) aeolian sands. Two smaller highs located in the west and south, separated from the eastern crest by a saddle and normal faults, were not drilled and were assumed to be in communication through the good quality reservoir and open intra-reservoir faults with the field crest in the east. The risk of fault sealing in the high permeability, high net reservoir was considered to be low. Initial gas production in 1999 of 100 × 10 6 SCFD was followed by a rapid decline to 15 × 10 6 SCFD early in 2001. This rapid decline suggests more complex reservoir geology than was anticipated, with barriers to field-wide reservoir communication occurring due to faulting or variation in reservoir quality. Geological, production and simulation data suggest that current wells located on the eastern crest are not accessing gas reserves elsewhere in the field due to sealing of major intra-reservoir faults. Field production has led to a significant pressure difference between the eastern fault compartment and the rest of the field. A horizontal well is planned to connect the western and eastern fault blocks and induce cross-flow of gas across the sealing fault into existing wells via the high permeability aeolian beds. The horizontal well will not be completed or tied back at surface and, hence, if successful, will be a low cost solution to increasing Dalton Field reserves.