110/2b-9: Dalton Field, East Irish Sea

Dalton is a gas field located in Block 110/2b at the north of the East Irish Sea Basin in the UKCS. Dalton was discovered in 1990 by well 110/2b-9 which encountered a dry gas column of 345ft 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 maximise recovery from the good quality reservoir (average permeability >50 mD). Production tests showed the majority of flow from the wells to come from thin high permeability (>200 mD) 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 as low. Initial gas production in 1999 of 100 mmscf/d was followed by a rapid decline to 15 mmscf/d 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. Understanding of well underperformance was gained by reservoir remodeling. 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 the generation of a significant pressure differential c. 600 psi between the eastern fault compartment and the rest of the field. An innovative infill well solution to harness this pressure differential, and induce cross flow across the sealing fault into existing wells via the high permeability aeolian beds is underway. The horizontal well will not be completed or tied back at surface, and hence, if successful will be a neat, low cost solution to increasing Dalton field reserves.