Feasibility Study of Gas Injection in Low Permeability Reservoirs of Changqing Oilfield

Abstract

Changqing Oilfield is the largest petroleum-producing field in China and one-third of its oil production is attributed to the formations with permeability lower than 1 mD. The rapid oil rate decline and low recovery factor (RF) associated with those formations require additional IOR/EOR measures besides waterflood. Based on the promising results from recent gas injection pilots in North America, we investigated the feasibility of gas injection in the low permeability formation (Chang 63) of Changqing Oilfield. An eight-component fluid characterization, which fits both the constant composition expansion (CCE) test and separator test, was used in a numerical dual-porosity compositional model. A typical well pattern, composed of six vertical injectors and one horizontal producer, is selected for the modeling study. The input parameters, including relative permeability, fracture permeability, etc., were adjusted to achieve an acceptable history match of the production data. Huff-n-Puff using several gases—lean gas (CH4), produced gas, rich gas (C2H6), and solvent (C3H8)— were investigated and the results were compared with the current waterflood. The simulation results show that the richer the injected gas, the higher the oil production. C3H8 huff-n-puff achieved the best performance, increasing the cumulative oil production by a factor of 2.28 after 5 cycles, then followed by C2H6 as 1.34, produced gas as 1.08. CH4 alone demonstrated a lower recovery factor than waterflood, because its minimum miscibility pressure (MMP) is close to the maximum allowable injection pressure, i.e., the minimum horizontal stress. In addition, the horizontal producer was completed at the reservoir top and water injectors were placed at the bottom, which was originally designed to improve the waterflood by gravity segregation. Under such well placement design, the miscible oil bank, which forms at the injection front during vaporizing drive, will be displaced towards the reservoir bottom even out of the SRV, undermining the huff-n-puff performance. Injection with rich gas will be more compatible, as the miscible bank forms at the injection tail. Injecting produced gas enriched with C3H8 will hence achieve promising EOR performance. The simulation also shows that increasing injection pressure increases the recovery factor. The leaner composition of produced gas could be compensated by a higher injection pressure. The optimal injection duration and soaking time could also be obtained after sensitivity analysis. Another critical factor is the fracture network characterized by the dual-porosity model, as simulation with the single porosity model only shows minor improvement in RF even with C3H8. Our work confirmed the technical feasibility of injecting rich gas in the low permeability Chang 63 by compositional simulation. We also determined the key parameters for the operator to consider in the next phase of the project.

A Visual Analytics Framework from Geological Modeling to Reservoir Simulation

“…The Y284 tight oil reservoir is located in the Changqing oilfield in Ordos Basin China and is used as an example data set in this project. By the end of 2017, the Y284 Unit [58] had 756 producers and their main producing layers lie in the third sub-member of the sixth member of the upper Triassic Yanchang formation also known as Chang 63 (C63), which contains green-greyish siltstones with dark grey mud intercalation [59] . The average air permeability without confining pressure is estimated as 0.38 mD.…”

Experimental Investigation on Cyclic Huff-n-Puff with Surfactants Based on Complex Fracture Networks in Water-Wet Oil Reservoirs with Extralow Permeability

“…The oil far away from the channeling fractures remains unswept in place. Therefore, the technology of huff-n-puff for a single well can be an excellent substitute to recover the oil near the well and the fractures [18][19][20][21], particularly during the early production period. Huff-n-puff covers the injection, soaking, and production cycles, which requires substantial water transfer into or out of the oil formation [8].…”

High-Precision Numerical Simulation on the Cyclic High-Pressure Water Slug Injection in a Low-Permeability Reservoir

“…About 38% of the global and 46% of China's oil and gas resources are of low quality mainly in low-permeability reservoirs, which need to be effectively developed to ensure sustainable development worldwide [1][2][3][4]. In recent years, with the exploration and development of unconventional oil and gas, numerous studies on the efficient development of low-permeability reservoirs have been done by many researchers [5][6][7][8][9][10][11]. With the application of horizontal well, multistage hydraulic fracking and acidizing, synchronous/asynchronous water injection, advanced water injection, lay-ered water injection, and other techniques, the lowpermeability reservoir is commercially and sustainably developed [12][13][14][15][16][17][18][19][20][21].…”