Hydraulic fracturing potential of tight gas reservoirs: A case study from a gas field in the Bredasdorp Basin, South Africa

Abstract

The issue of hydraulic fracturing in the onshore Karoo Basin has triggered an intense political, social and environmental debate in South Africa. This research paper proposes the relatively under-explored F–O tight gas field in South Africa as a demonstration site that can shed light on the ongoing debate on the use of hydraulic fracturing in the Karoo Basin. By combining petrographic and geomechanical analyses with critical velocity experiments and rock mechanics testing, a step-by-step guide for assessing the hydraulic fracturing potential of tight gas reservoirs was presented. K-Means clustering was used to improve the sampling strategy and to capture reservoir heterogeneity. The results obtained showed that K-Means clustering improves reservoir characterisation by revealing heterogeneous intervals, thus optimising petrographic and geomechanical analyses. In addition, the hydraulic fracturing fluid was found not to cause formation damage in the reservoir at a critical velocity of 0.155 ml/min. The elastic properties also showed that the F–O Tight Gas Field has a high degree of brittleness with good hydraulic fracturing potential. Finally, the characterisation of the fractures shows that partially open fractures are prevalent, which can dilate under the high differential stresses in the reservoir. Although further investigation is required, this study has shown that the F–O gas field is a promising candidate for hydraulic fracturing.