Overview Of Offshore Horizontal Drilling/Completion Projects In Unconsolidated Sandstones In The Gulf Of Mexico
Authors: McLarty J.M. , Dobson J.W. , Dick M.A. 
Published: October 2008

In the last two years much progress has been achieved in the field of horizontal drilling in unconsolidated reservoirs. Horizontal completions have become a common, successful, and economical method to produce unconsolidated reservoirs. This paper outlines the techniques used to drill and complete seven horizontal wells in the Gulf of Mexico over the last two year period. All of the wells are currently producing at or near the anticipated productivity levels and all have produced at rates considerably higher than vertical offsets.

The wells were drilled using a concept that linked the drilling and completion phases together to streamline the total operation and minimize the potential for formation damage. The concept is based on the premise that the drilling stage should not cause any damage that cannot be removed in the completion stage. This allows the well to be completed as an open hole and greatly simplifies the procedures involved.

The procedures which were used do not require the wells to be cased, or perforated and the only sand control which has been implemented is a mechanical screen across the open hole interval. The wells were drilled with a fluid containing solid sized salt particle bridging agents and a series of clean-up procedures that provide a very economical completion. This paper describe the guidelines that were used on the completions and also elaborates on the problems which were encountered to allow knowledge to be gained from the concerns which have been addressed by these projects.

UNCONSOLIDATED CONCERNS

The main concerns which have to be addressed when designing a drilling/completion strategy for a horizontal wellbore in an unconsolidated sand are:wellbore instabilitycuttings transportdrilling fluid displacementminimizing formation damage

Wellbore instability was one of the primary concerns when the first horizontal wells were planned. A great deal of research has been conducted on the subject and the ability of the fluid to form a low permeability filter cake which is not easily eroded during the drilling process has been found to be essential to maintaining the integrity of the wellbore.1 High angle drilling projects are also plagued by the problem of cuttings transport. The turbulent flow profile required to transport the cuttings beds could result in erosion of the filter cake which will therefore, decrease the wellbore stability. Higher viscosity flow profiles have been determined to minimize this problem by allowing similar hole cleaning capability with Iaminar flow regimes2 that will carry the cuttings adequately and also help to prevent cutting beds from forming. Another objective is to minimize the potential for formation damage. The mechanical configuration of a horizontal wellbore could be greatly simplified if the horizontal section did not require casing or perforating. If the drilling damage can be minimized, there is no reason to perforate past the damage zone. This would simplify the configuration and enhance the productive potential of the wellbore by allowing the increase in surface area provided by an open hole completion.