Effective Ways to Avoid Barite Sag and Technologies to Predict Sag in HPHT and Deviated Wells With a Case Study in One Iranian Reservoir

Abstract

Barite sag is an oilfield term used to describe significant density variations while circulating bottoms up after a trip, logging run, or other operations that require the mud to remain static for an extended period of time. Sag is caused by static or dynamic settling followed by slumping of the weighted material. Static sag, as the name suggests, is caused when circulation is stopped for an extended period of time and the weighting agents begin to settle under the influence of gravity. The authors present the most effective ways to avoid the occurrence of barite sag in high-pressure high-temperature drilling operations, and in high-angle wells beside a case study in Gachsaran formation in Ahwaz oil field of Iran. The ways involve replacing barite by other weighted materials such as ilmenite or manganese tetraoxide. The lower the Equivalent Circulating Density, the higher the rate of drilling operation as well as the lower pressure losses, especially in mud pumps. In this thesis, a new water-based mud formulation is introduced that uses polyanionic cellulose and xanthan gumas viscosifiers. By using a Brookfield viscometer (DV-II + Pro), viscosities of different muds at ultralow shear rates were measured. According to their rheological properties, a desirable mud formulation was developed.