Mitigating Clay Sensitivity in Heavy Oil Recovery: A High-Intensity In-Situ Combustion Strategy with a Case Study of Block J10, Shengli Oilfield

Summary

The J10 block in Shengli Oilfield is a clay-sensitive heavy oil reservoir. Steamflooding and cyclic steam stimulation were used in this field but showed limited effectiveness. Therefore, in-situ combustion (ISC) field trials were subsequently implemented. However, operational challenges emerged; namely, difficult ignition and unstable combustion-front propagation. For this study, we established a multiscale experimental framework combining high-pressure differential scanning calorimetry (HPDSC), ramped temperature oxidation (RTO), and combustion-tube experiments. This framework was used to evaluate the effects of clay content on the oxidation behavior and combustion stability of heavy oil. Subsequently, the technical feasibility of ISC in clay-sensitive heavy oil reservoirs was validated using this particular heavy oil sand as an exemplar. Results demonstrate that elevated clay content in the rock exerts a dual-effect mechanism on ISC performance. Specifically, the presence of clay minerals in the rock decreases the activation energy of heavy oil oxidation and accelerates the oxidation reactions. Meanwhile, conversely, elevated clay content reduces the porosity and permeability of the reservoir rock, thereby impeding the advance of the combustion process. At 20% clay content, the activation energy for the low-temperature oxidation (LTO) reaction drops from 69.95 kJ/mol to 51.21 kJ/mol, while it drops from 233.52 kJ/mol to 157.31 kJ/mol for the high-temperature oxidation (HTO) reaction. However, this catalytic activity reduces the amount of HTO heat released from 53.7% to 36.3%. This behavior significantly alters ISC performance. Reaction pathways shift toward lower temperatures. The high-temperature combustion zone is destabilized. The peak combustion temperature drops from 571.2°C to 524.4°C, and the ignition time is prolonged, manifesting the characteristic behavior of “easy oxidation yet difficult ignition.” Combustion-tube tests confirmed successful ignition at 400°C. Clay-sensitive heavy oil required significantly higher air flux [212.2 m³/(m²·h)] to sustain stable combustion, compared with conventional reservoirs. Ultimate oil recovery reached 81.8%. Substantial crude upgrading was evidenced by the saturated hydrocarbon content increasing from 36.15% to 59.52%. These findings elucidate the coupled clay-oxidation-combustion mechanism and support a “high-temperature ignition with elevated-rate air injection” strategy. This approach provides design criteria that successfully guided field-scale ignition operations in two well groups.