Fracturing in a Tectonically Stressed Area under Anomalously High Gradients

Abstract

Abstract Increasing depth of exploration wells usually results in elevated fracturing gradients and decrease of permeability of the formations. Adding tectonic stresses and well deviation to these conditions may result in a distorted stress field with anomalous fracturing and breakdown gradients, thus causing multiple complexities. In case studies, 11 fracturing treatments performed at high fracturing gradients in the same oil field were analyzed, and the following complicating factors were distinguished: high treating pressures, anomalous breakdown gradients, inability to place planned amount of proppant due to near-wellbore complexity, accelerated leakoff in opened fissures, and accumulation of the stress at the formation with each successive pumping cycle. These factors can be attributed to the combination of the reservoir properties, well placement, and well completion techniques: high tectonic stress is a basic cause of increased fracturing pressures, well deviation is a substantial contributor to the increase in the breakdown pressures, reservoir poroelastic properties are the reason for the accumulation of the back-stress, and perforation strategy is the key factor in the near-wellbore complexity. An explanation of each factor is given in the current paper, with the case study examples. Prevention and mitigation measures are proposed, based on the experience from the considered cases and literature review.