Study of materials to combat loss of circulation in fractures and static filtration

Abstract

For the obstruction and reinforcement of permeable rocks (pores and or fractures), materials to combat loss of circulation (LCMs) are commonly used in the drilling fluid. LCMs, when forming bridges, support and seal rocks, with the objective of preventing drilling fluid from reaching the reservoir. In this study, drilling fluid formulations were developed using full four-level factorial design (DOE), with a central point (4 ^ 2 + 3) in order to evaluate the effect of drilling fluid components on their rheological properties and in the loss of circulation. The tested fluids were prepared using carboxymethylcellulose polymer (CMC), bentonite (BT) as a thickener, and the materials used to combat loss of circulation were used with diatomaceous earth (DE) and hydrogel (HG). The density and pH of all fluids were adjusted to approximately ≈1.14 g/cm−3 and 8.5, respectively, being named F(CMC)BT-DE-HG. The filtration experiments were performed in a HTHP (high temperature, high pressure) filtration cell and the fracture was sealed in a physical simulator, called Fracture Flow Simulator (SEF). The rheological data were adjusted using the Herschel Bulkley model. The incorporation of LCMs in the drilling fluid improved the rheological properties. The results indicated that the investigated factors CMC, BT and HG had the main effects in combating the loss of circulation in the fracture and filtration phases. Diatomaceous earth was not significant in filtration and fracture tests. Finally, based on rheological tests, it can be inferred that the interaction of HG*CMC and BT*CMC is highly significant in combating loss of circulation. The fluid with lower DE level showed superior performance, as it sealed the fracture in 1 min of testing and a low volume of filtrate was observed in the test.