Abstract

South Diana is a single-well gas condensate field in the deepwater Gulf of Mexico (GOM). The reservoir consists of turbidite unconsolidated sands separated by thin shales. Geomechanical characterization of South Diana core revealed high rock compressibility and potential for compaction- induced permeability reduction. This paper discusses various modeling studies conducted prior to field startup to assess the impact of rock compaction on well integrity and producibility. Geomechanical models, reservoir simulation studies, and core measurements were used to develop physics-based integrated well performance technical limits. These technical limits have been used to successfully manage rock compaction related risks to well integrity and producibility. Reservoir surveillance data and comparison with model predictions are discussed. Reservoir management issues and insights gained from field data for this compacting deepwater reservoir are also discussed.

Introduction

As offshore developments trend toward fewer wells with high per-well production volumes and rates, new technologies are required to ensure long-term mechanical integrity and optimum producibility of wells. An example of one such development is the South Diana single-well satellite gas field in deepwater GOM. The field was developed through an 8-mile subsea well tie back to existing infrastructure in the Diana Basin (4400-ft water depth). The reservoir consists of several high quality distal turbidite unconsolidated sands separated by thin shales. At the time of field development, key geologic uncertainties included connectivity across the reservoir area and sand thickness away from existing well control. Natural depletion with moderate water-drive is the expected depletion mechanism. Cores and fluid samples were obtained from the discovery well and a sidetrack well.

Geomechanical characterization of South Diana core revealed high rock compressibility with depletion and potential for compaction-induced permeability reduction. Pressure transient analysis from offset ExxonMobil operated reservoirs (Diana, Hoover, Marshall, Madison) within the Diana basin has confirmed reservoir-wide compaction. These analyses have shown reductions of up to 80% of the original flow capacity (Kh) for several wells. The quantitative impact of compaction could not be predicted directly from laboratory measurements on cores for a number of reasons including differences in stress paths between experimental and actual reservoir depletion. Similar compaction induced reduction of Kh has been documented by other GOM operators.

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