Experimental Investigation on Wellbore Strengthening Based on a Hydraulic Fracturing Apparatus

TLDR

Lost circulation remains a persistent issue in the petroleum industry, and wellbore strengthening with lost circulation materials (LCMs) is a widely used mitigation strategy. This study introduces a hydraulic fracturing apparatus to examine how LCM type, concentration, and particle size distribution affect wellbore strengthening. The apparatus analyzes pressure curve characteristics during fracturing to evaluate the strengthening effect of different LCMs. Results show that fracture pressure rises with LCMs, reaching a maximum at an optimal concentration; wide PSD LCMs markedly increase pressure, whereas narrow PSD LCMs can lower it, and pressure curves reveal distinct stages that guide the selection of LCMs to maximize peak pressure, extend stable pressure, and control instability.

Abstract

Lost circulation is a serious problem which always exists in the petroleum industry. Wellbore strengthening by lost circulation materials (LCMs) is a commonly applied method for mitigating lost circulation. This paper presents a hydraulic fracturing apparatus to investigate the effect of material type, concentration, and particle size distribution (PSD) of LCMs on wellbore strengthening behavior. In addition, the characteristics of pressure curves in the fracturing process are analyzed in detail. The results showed that the fracture pressure of the artificial core can be increased by LCMs, and there exists an optimum concentration of LCMs for the maximum wellbore strengthening effect. The LCMs with wide PSD can significantly increase the fracture pressure. However, some LCMs cannot increase or even decrease the fracture pressure; this is resulting from the LCMs with relatively single PSD that makes the quality of mud cake worse. The representative pressure curve in the fracturing process by drilling fluids with LCMs was divided into five parts: the initial cake formation stage, elastic plastic deformation stage, crack stability development stage, crack instability development stage, and unstable plugging stage. The actual fracturing curves were divided into four typical types due to missing of some stages compared with the representative pressure curve. In order to strengthen the wellbore in effective, good LCMs should be chosen to improve the maximum pressure in the elastic plastic deformation stage, extend the stable time of pressure bearing in the crack stability development stage, and control the crack instability development stage.