Experimental and Numerical Investigation of Characteristics of Highly Heterogeneous Rock Mechanical Responses in Tight Sandy Conglomerate Reservoir Rock Under Tri-axial Compression

Abstract

Due to the use of horizontal wells and hydraulic fracturing, commercial tight oil production from some tight sandy conglomerate reservoirs has been achieved. Since the widely distributed gravels in the sandy matrix in conglomerate reservoir rocks are harder than the matrix, the rock mechanical response in conglomerates under compression is highly heterogeneous. This increases the complexity of understanding the hydraulic fracturing behaviors in conglomerate reservoirs. Previous tri-axial compression tests provided the stress-strain relationships of conglomerate samples as a whole, and the stress and strain in the gravels and in the sandy matrix were not investigated due to the limitation of the compression test lab. This study presents tri-axial test results for a conglomerate sample cored from a reservoir that has been economically developed. Lab results are then used to calibrate the numerical model for the simulation of the tri-axial compression process. Numerical results indicate that the elastic modulus and size of gravels have significant impacts on the axial stresses and axial strains in the conglomerate. Stress concentrations are observed in gravels due to the heterogeneous mechanical properties in the conglomerate. The reorientation of the maximum horizontal principal stress is quantified to study the mechanisms of the interaction types between hydraulic fractures and gravels embedded in the tight sandy matrix.

Effects of parent well spacing on the poroelastic behaviors in the infill zone in shale oil reservoirs: A case study in Jimsar Shale Oil, China

“…For the infill zone, the 200 m well spacing results in very insignificant reorientations, while the 300 and 400 m well spacing scenarios lead to certain reorientations. Therefore, for the 300 and 400 m well spacing scenarios, a future infill well fracturing job can experience greater frictional loss within the fractures during pumping, as the likelihood of non‐planar fracture growths is higher in these cases with more reorientations in the principal stress field 34,35 . Combined with the observation in Figures 8‐10, it is estimated that, although the pore pressure is largely depleted in the infill zone, the 200 m spacing can reduce the energy required to establish infill well fracture networks.…”

“…Log interpretations and rock mechanical tests are used to determine these mechanical properties, where typical logs such as acoustic logs, resistivity logs, and GR logs are used in the interpretation, and tri-axial tests are used for elastic property evaluation. 34,35 The permeability of the matrix is 0.047 mD with a porosity of 8. pressure values at hydraulic fractures are all equal to the depletion pressure of 25 MPa. After 12 months, pressure depletion is mainly contained in SRVs and the infill zone only has slight pressure decreases.…”

“…A tensile strength value of 10 MPa is obtained. Log interpretations and rock mechanical tests are used to determine these mechanical properties, where typical logs such as acoustic logs, resistivity logs, and GR logs are used in the interpretation, and tri‐axial tests are used for elastic property evaluation 34,35 . The permeability of the matrix is 0.047 mD with a porosity of 8.4%.…”

The experimental and numerical analysis of elastic rock mechanical properties in tight conglomerate rock samples: a case study in Junggar Basin

“…Tight oil reservoirs in this region have been commercially developed (Wang et al, 2022a;Wang et al, 2022b). The implementation of horizontal well drilling and hydraulic fracturing has largely improved the productivity here (Chen et al, 2021b;Zhi et al, 2021). Unlike tight sand reservoirs or shale reservoirs, tight conglomerate reservoirs have strong heterogeneities caused by the existence of gravels.…”

A study of effects of different impact loads on the dynamic and elastoplastic behavior in reservoir rocks at the beginning of hydraulic fracturing

“…Experimental and numerical studies of the rock mechanical behaviors are relevant since they can help to determine the essential elastic and plastic properties of reservoir rocks. These properties are related to the hydraulic fracturing processes since they usually govern brittleness and fracability (Lecampion et al, 2018;Chen et al, 2021b;Guo et al, 2021b), and they are often correlated with the fluid flow and rock deformation behaviors in the hydrocarbon-bearing formations (Guo et al, 2023). Zhang et al (2021) proposed an experimental method to quantify the effect of loading rates and lithologies on Kaiser effects during in-situ stress measurements, where loading rate selection criteria are determined.…”