Development drilling normally involves less risk since many drilling parameters are known; however, in mature fields operating under depletion or limited water drive mechanisms, this is not always the case. Although the reservoir pressures are known, depleted sands can present serious drilling problems and substantial cost increases. Differential sticking of drill pipe, casing, and logging tools; and tight hole conditions due to excessive filtrate loss and cake buildup are some of the problems which may occur. Additional casing strings may also required to cover these sands. Effectively plugging the depleted intervals is the key to preventing most of these problems.

Experience has been limited drilling through numerous, severely depleted sands for prolonged periods. The focus of this paper will be upon the well design and water-based drilling fluid considerations which have proven successful under these conditions. Drilling practices, specially designed plugging products used, and research developments in plugging permeable formations using a new test apparatus will also be presented. Application of these practices should prove effective in any geologic area containing normal sandstone-shale sequences such as the Gulf of Mexico.

Three examples of the most extreme case histories will be exhibited. These wells had sands which were exposed to differential pressures exceeding 4700 psi with as many as ten sands and differentials over 2500 psi exposed at one time. To further complicate matters, all the wells were directionally drilled with hole angles ranging from 20 to 42 degrees.

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