Estimation of proppant embedment from laboratory instrumented indentation tests on Montney formation in Western Canada

Abstract

Instrumented indentation tests have been gradually adopted to rapidly characterize mechanical behaviours of tight formation rocks, which provides valuable data for estimating proppant embedment in hydraulic fractures. This paper presents a laboratory study on Montney formation samples from depths between 2068 and 2337 m using both instrumented indentation tests and proppant embedment tests, which is the first of this kind to have both tests conducted on the same formation rock and depths for facilitating direct comparison. Fifty-six indentation tests show that Young's modulus and hardness of Montney formation are strongly related to the elastic indentation and the total indentation, respectively. Indentation tests can over-estimate the local Young's modulus when there are large fluctuations in the unloading indentation depth vs. force curves. Hardness, commonly assumed to be constant, is found to change with the indentation depth and can be related to the impression area on the rock surfaces with a power function. The proppant embedment test results show that the reduction in the proppant-propped fracture aperture with closure stresses is analogue to the indentation force vs. depth curves. Some proppant embedment tests have abnormal results due to either the puncture of sample membrane sleeves or uneven proppant placement between fractures, which highlights the challenges of conducting proppant embedment tests. To utilize the results from efficient indentation tests for estimating fracture aperture changes with compressive stresses, a mathematical model considering proppant deformation and proppant embedment was proposed for fractures propped with monolayer proppants. The mathematical model gives an excellent prediction of fracture apertures under various stresses that match the laboratory proppant embedment measurements. The usefulness of the indentation tests and the mathematical model is further demonstrated by determining the model parameters for Montney formation rock treated with two fracturing fluids, which offers an alternative approach to expensive proppant embedment tests.