Recovery Optimization by Modeling Depletion and Fault Block Differential Pressures at Green Canyon 110
Authors: Kikani Jitendra , Smith T. Dirk 
Published: December 2007

A robust depletion/completion strategy for deepwater subsea wells is critical to the economic success of a project. Since recompletions are expensive and risky, commingling different horizons or fault blocks could be attractive. This option is now available due to recent regulatory policies which have moved away from specific reserve limits as a criteria for commingling.

This paper describes the methodology and the results of a simulation study performed to evaluate the development options for Shell Offshore Inc.'s (SOI) first modern technology subsea oil well at Green Canyon (GC) 110 - a satellite development to Bullwinkle located in the same basin. The well SOI GC110-4 cutting across a fault at an angle of about 620, indicated the existence of pressure differentials between the upthrown and downthrown blocks at current conditions. The two fault blocks communicate with each other through a common aquifer. At a datum depth of -11000 ft SS, the reservoir is depleted by about 750 psi compared to the well GC110-2 which was drilled in 1987 prior to the start of production from Bullwinkle.

The seemingly fragmented data was reconciled into a reservoir model by accounting for basin depletion effects. A hypothesis about the reservoir and fault connectivities was used to address dynamic model initialization. A first order material balance estimate of basin depletion based on prospect Bullwinkle production data was used to tune the model. The model was constrained to provide two unique initializations that honored four independent pieces of data. The current conditions in the reservoir were matched honoring all the data constraints. Based on this dynamic initialization, a completion strategy was developed.

A number of development scenarios including sequential and commingled production as well as the effect of shutin on crossflow were considered. The results indicate that it will be prudent from the recovery and economic perspective to commingle the two fault blocks through GC110-4. This scenario provided the highest recovery at the lowest life cycle cost. An application for commingling was made to the MMS and the approval was received. The well is currently on production at anticipated rates.

Introduction

Green Canyon 110 is situated in 1800 feet of water in the Gulf of Mexico. The prospective interval contains a series of sands and mudstones deposited by low-relief submarine channels. Oil is encountered in turbidite sands of early Pleistocene age at approximately -11000 feet subsea depth. This prospect is being developed as a single-well subsea satellite to prospect Bullwinkle and is tied back to the platform at Bullwinkle. Figure 1 shows the location and geological structure of GC110 and the associated mini-basin. As can be seen, GC110 is part of the same basin as Bullwinkle and lies in the southeast corner. The sands pinch out along the eastern flank where they lap onto the basin margin.

Hydrocarbon resource at GC110 is about 13.2 MMSTBO and 29.4 BCF of gas. A large active aquifer connects to the reservoir. The reservoir is divided into three fault blocks by east-west trending faults. Only one fault which cuts the apex of the reservoir has a significant throw and is a scissors type fault with sand-on-sand contact in the aquifer region.

The objective of the current study was to incorporate data from the development well GC110-4 to update the existing reservoir model and to prepare a case for approval from the MMS on the preferred choice of a development system.

History

Three exploratory wells were drilled in the late 1980's.

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