As oil and gas fields become mature, there is an increasing need to drill, complete and workover wells in depleted zones. The proximity of normally pressured zones often means that, in order to maintain wellbore stability, the depleted formations experience very high overbalance pressures – often exceeding 1000psi. As a consequence, problems such as differential sticking, deep filtrate invasion and severe lost circulation are common. In the extreme, increased costs and high levels of formation damage can make continued exploitation of fields uneconomic.

This paper describes a new fluid additive package designed to form an effective, low permeability barrier on permeable formations. The materials have been used in a wide range of water, oil and synthetic based fluids with excellent results. We present laboratory evidence and field data to show that fluid invasion is greatly reduced. This brings several important benefits:

  • Differential sticking is greatly reduced

  • Fracture gradients are increased (increases well over 1000psi have been observed).

  • Return permeability results, and hence well productivity indications, have been excellent.

The paper discusses the mechanism by which the additives provide superior invasion control, and the ease with which the protective barrier is removed from producing intervals.

The materials have been used onshore and offshore in most major oil and gas provinces. In addition to providing effective technical solutions, they have the environmental approvals that allow their unrestricted use in areas such as the Gulf of Mexico and the UK North Sea.

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