An integrated approach was applied for production enhancement of the upper and lower shaly sandstone reservoirs of the Ignalinsky and Tympuchikansky fields in the Leno-Tunguska oil and gas province of the East Siberian Basin, Russia. The approach includes both comprehensive laboratory studies and a direct strategy of hydraulic fracturing design, as well as solutions to obtain optimum well performance. The approach can be implemented in future prospects and can form part of the strategy for future development in the region.
Extensive laboratory research was performed to select the proper fluid for proppant transport that could withstand all the complicated terrigenous conditions within the fields. One of the main challenges was rheological suitability of the fluid at low reservoir temperatures. The laboratory studies were important for identifying the best fluid for fast fracture cleanup while optimizing the sand-carrying capacity of the fracturing fluid. The hydraulic fracturing design incorporated calibrated petrophysical and geomechanical analysis with actual fluid rheology characterization taken from laboratory test results.
The laboratory work confirmed that the reservoir rock was water sensitive, with a significant presence of clay minerals including kaolinite, montmorillonite, and montmorillonite mixed with illite. A new generation of clay stabilizer was used to address this sensitivity. In addition, an enzyme breaker was used with the objective of effectively breaking the fracturing fluid at low reservoir temperatures. The fracturing operations that were performed during two winter campaigns resulted in high starting and operating production rates. The treatment designs incorporated a linear gel pre-pad stage prior to the crosslinked pad stage in an effort to extend fracture half-length while reducing the risk of the fracture growing in height into overlying gas-saturated layers. The results of the design efforts were analyzed using logging and fracture treatment data, which demonstrated that the design was effective in avoiding the gas-saturated formation. Overall, 23 hydraulic fracturing operations were done in five wells at Ignalinsky and Tympuchikansky fields for the B10 and B13 formations. Production results were analyzed, and further optimization paths were identified.
The study breaks new ground in enhancing the hydrocarbon extraction from low-temperature shaly sandstones with mixed wettability, not just with terrigenous reservoirs within the above-mentioned fields, but also with other reservoirs of a similar geological context, primarily the Leno-Tunguska oil and gas province of the East Siberian Basin, Russia. This is especially important in view of the depletion of oil reserves in Western Siberia and the growing interest in the development of hydrocarbon fields in Eastern Siberia.