The Best Common Ways to Manage Barite Sag in HPHT and Deviated Operations With a Case Study in the Iran Oil Industry

Abstract

Barite sag is an oilfield term used to describe significant density variations while circulating bottoms up after a trip, logging run, or other operation that requires 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 circulating is stopped for an extended period of time, and the weighting agents begin to settle under the influence of gravity. Due to slumping, dynamic sag occurs frequently in inclined holes. However, the problem has been exacerbated by the increased frequently of high-angle wells with the associated increase in particle settling rate, which occurs in an inclined fluid column. The settling of solids is enhanced by convective currents created by density differences in the fluid across the annulus cross-section. This effect is frequently referred to as the Boycott effect. 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 the Ahwaz oil field of Iran. The methods include replacing barite with 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. The authors introduce a new water-based mud formulation that uses attapulgite and xanthan gum as viscosifiers. By using a Brookfield viscometer (DV-II C Pro), viscosities of different muds at ultralow shear rates were measured. According to their rheological properties, a desirable mud formulation was developed.

Enhancing Hematite-Based Invert Emulsion Mud Stability at High-Pressure High-Temperature Wells

“…The solid particles settling is a common issue encountered in high-pressure high-temperature (HPHT) conditions where downhole temperature is greater than 300 °F in both vertical and deviated wells and known as solids sag. − This sagging issue is affected by the drilling fluid properties such as the low viscosity, fragile gel strength, low linear viscoelastic, solid particles characteristics, and drilling parameters, and it may eventually result in wellbore instability, stuck pipes, and loss of circulation due to the wide variation in mud properties. − The sagging issue becomes more serious at an inclination angle above 30°, and the maximum sagging was observed to occur in the range of 45 to 60° wellbore inclination. ,, …”

Micro-manganese as a weight agent for improving the suspension capability of drilling fluid and the study of its mechanism

“…Among them, the performance of drilling uids is closely related to the selection of weighting materials. 6,7 Barite is the most commonly used weighting material to adjust the density of drilling uid. However, the problems of lter cake thickening, increasing equivalent circulation density (ECD), excessive torque and friction caused by barite sagging oen occur.…”