High-pressure high-temperature (HPHT) reservoirs required special drilling fluid with high density and steady rheology to sustain the challenging conditions. Barite is one of the most weighting agents to increase the mud density at a low cost. But drilling HPHT wells causes settle the barite particle down in the wellbore known as barite sagging. Barite sagging may lead to several issues, for instance, stuck pipe, density variation, loss of circulation and well control problems.

To prevent the barite sagging, a new copolymer was used in this study. Static sag experiments were conducted to evaluate the mud in drilling break for both cases vertical and 45° inclined wells, dynamic sag tests also were performed to simulate the sagging while drilling. Static and dynamic sag tests were conducted to evaluate the ability of copolymer to suspend the weighting materials in the invert emulsion drilling fluids (IEF). Then the effect of adding copolymer in rheology, electrical stability, and HPHT filtration was achieved.

The objective of this study is to assess the effect of adding the new copolymer to IEF (polymer based on styrene and acrylic monomers) on the suspension efficiency of the weighting agent and rheological stability in HPHT condition

The results obtained showed that 1 lb/bbl of the new copolymer didn't affect the electrical stability of the invert emulsion mud. The sag issue was prevented after adding 1 lb/bbl of the copolymer for both vertical and inclined situation and in the dynamic case at a temperature greater than 300 °F. For the rheology test, the copolymer enhanced the plastic viscosity, yield point and gel strength of the mud to increase the mud stability during drilling HPHT wells. Adding 1 lb/bbl of copolymer had no effect on HPHT filtration loss and filter cake thickness.

The novelty of this study is to provide the oil and gas industry with newly designed mud to solve the barite sagging for the invert emulsion drilling fluid at high density to sustain the HPHT.

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