This study investigates the impact of different injection media and gas injection methods on oil recovery in the Fuman Oilfield within the Tarim Basin, aiming to optimize gas injection strategies for enhancing oil recovery in the Manshen 4 well area, known for its light, low‐viscosity, low‐sulfur volatile oil and stable strata thickness. The research employs experimental analyses to assess the miscible displacement characteristics of nitrogen, hydrocarbon gas, and carbon dioxide under varying pressures. Findings show that nitrogen achieves miscible displacement at higher pressures (47.5 and 45 MPa), whereas carbon dioxide has the lowest minimum miscibility pressure (MMP). Hydrocarbon gas shows miscibility at intermediate pressures (44 and 41 MPa). In the early stages of gas injection, nitrogen is most effective due to its ease of achieving miscibility. For later stages, hydrocarbon gas and carbon dioxide are more beneficial because of their enhanced solubility and miscibility with the volatile oil, leading to increased recovery rates. The study recommends a strategy combining top nitrogen injection–bottom water injection, and mid‐level oil production to maximize recovery efficiency and maintain optimal production levels. This study innovatively combines different gas injection media at different injection stages and proposes a top nitrogen injection–bottom water injection and mid‐level oil production strategy, which is a new attempt in enhancing oil recovery in similar volatile oil reservoirs. It provides a more comprehensive and efficient solution compared to previous single‐medium injection methods. These results offer valuable guidance for the Fuman Oilfield and similar geological settings.
Static gas–water relative permeability curves are widely used to evaluate productivity in low‐permeability water‐bearing sandstone gas reservoirs, but treating these curves as fixed can overestimate deliverability during the middle and late production stages. Field production and pressure data provided by the operating company indicate that the principal near‐wellbore displacement pressure gradient in the target reservoir is 12–28 MPa/m. Gas–water relative permeability experiments were therefore conducted under reservoir conditions at 10, 20, and 30 MPa/m using a Huagang Formation core from the Xihu Depression, with the three levels bracketing the field‐relevant range. Increasing displacement pressure gradient reduced residual gas saturation, increased endpoint water relative permeability, and expanded the gas–water coflow region. We established a gradient‐controlled Corey model and implemented it through a local gradient–based calling rule in a gas–water two‐phase nonlinear productivity model that also incorporates threshold pressure gradient and stress sensitivity. Sensitivity analysis showed that threshold pressure gradient shortened the stable production period, stress sensitivity progressively weakened reservoir gas supply, gradient‐controlled relative permeability variation accelerated the loss of effective gas‐phase flow capacity during the middle and late stages, and increasing movable water saturation further shortened stable production and aggravated late‐stage decline. Field applications to Wells A1–A4 showed that the model can characterize the main productivity‐evolution trends, with whole‐period cumulative production deviations of 1.89%, 9.99%, 9.26%, and 2.60%, respectively. The model is intended for rapid evaluation of single‐well productivity trends under comparable local reservoir conditions rather than detailed field‐scale reservoir simulation.
Submarine gas seeps at Anchorage Cove in George Sound document fluid migration along the submerged Australian‐Pacific plate boundary in Fiordland, New Zealand. Gas samples from shallow seafloor vents (< 8 m) are dominated by N₂ (~96%), with minor O₂, Ar and CH₄. He concentrations (~0.27%) are approximately 500 times above air‐saturated equilibrium values. CO₂ concentrations fall below expected atmospheric contributions, and H₂ is effectively absent. Stable isotope values indicate a predominantly atmospheric origin for nitrogen ( δ 15 N ≈ +0.5‰), whereas corrected N₂/Ar ratios are elevated relative to the atmospheric value, consistent with a minor nonatmospheric nitrogen component. Methane is 13 C‐enriched ( δ 13 C‐CH₄ ≈ +11‰), potentially reflecting methane oxidation during shallow fluid circulation. Helium isotope ratios reveal a mantle‐derived contribution, with 3 He/ 4 He ratios of 1.96–2.12 Ra and elevated 4 He/ 20 Ne ratios indicating approximately 20%–30% mantle‐derived helium within the nonatmospheric fraction. 40 Ar/ 36 Ar ratios are also above atmospheric values. Despite this mantle helium signal, CO₂ concentrations fall below atmospheric levels, resulting in He‐CO 2 decoupling, with CO 2 / 3 He ratios approximately five orders of magnitude below the mantle reference value. This decoupling indicates substantial postsource modification of the gas, potentially through CO₂ dissolution and carbonate precipitation during fluid migration. The distribution of seepage is consistent with structurally controlled fluid discharge, although a direct connection with the George Sound Shear Zone cannot be established from the available observations.
In the process of deep mining in the Jurassic coalfield of the Ordos Basin, the key bottleneck in preventing and controlling roof water inrush disasters is the unclear dynamic evolution mechanism of hydrogeological parameters of the roof aquifer under the coupling of mining stress and seepage. Existing studies mostly focus on a single process—either mining-induced overburden failure or seepage field evolution—and lack systematic clarification of the quantitative evolution law of hydrogeological parameters throughout the full mining cycle, as well as the intrinsic response mechanism between overburden failure and seepage field evolution, with insufficient engineering-scale in situ verification results. Taking the No. 3-1 coal seam of Mudu Chaideng Coal Mine in the Hujierte Mining Area of the Ordos Basin as the research object, this study adopted a combination of in situ hydrogeological tests, long-term sequential monitoring, FLAC3D numerical simulation, Visual MODFLOW flow field inversion, and multifield coupling theoretical analysis to systematically reveal the spatiotemporal evolution law of hydrogeological parameters of the roof aquifer under the coupling of mining stress and seepage. The research results indicate that the sandstone aquifers at the bottom of the Zhiluo Formation and in the Yan'an Formation are the main water-filling aquifers, which can be connected by the mining-induced water-conducting fracture zone (WCFZ). The WCFZ has a maximum development height of 95.80 m, with a “saddle-shaped” spatial distribution, and its development process exhibits three-stage characteristics, forming a dominant channel for groundwater seepage. After mining, the cumulative water level drop of the target aquifer exceeds 400 m, and the average increase rate of the permeability coefficient reaches 54.77%. The mine water inflow shows three-stage evolution characteristics, with lateral runoff of the aquifer as the core recharge source during the stable period. This study clarifies the whole-chain response mechanism from mining-induced overburden failure to mine water inflow evolution, improves the theory of mining-induced seepage evolution in Jurassic thick-bedded sandstone aquifers, and provides a scientific basis for the precise prevention and control of roof water hazards and dynamic prediction of water inflow in fully mechanized mines with Jurassic near-horizontal medium-thick coal seams at a buried depth of 600–700 m.
Mining-induced damage to a narrow retained coal pillar can establish preferential air leakage pathways between an active goaf and an adjacent previously mined goaf, thereby altering oxygen transport and the spatial distribution of residual coal oxidation regions. Taking the 31119 gob-side entry driving panel of Nalinhe No. 2 Coal Mine as the engineering background, this study combined buried tube monitoring, gob-side directional borehole sampling, and CFD porous medium simulations to investigate the effects of retained coal pillar damage on airflow and oxygen migration. A coal pillar damage–air leakage–oxygen transport model was established, and steady-state simulations were conducted for different prescribed coal pillar damage conditions. Field monitoring showed that the oxygen-defined oxidation zone in the 31119 goaf extended from 37.5 to 83.9 m on the intake side and from 16.2 to 49.0 m on the return side, whereas the corresponding simulated ranges were 35–84 m and 16–51 m, respectively. More importantly, in the adjacent 31120 goaf, the monitored oxidation zone range along the gob-side strike direction was approximately −45 to 14 m, compared with a simulated range of −48 to 13 m. With increasing retained coal pillar damage, fracture connectivity and equivalent permeability increased, promoting deeper oxygen penetration and progressive expansion of the oxidation zone in the adjacent goaf, whereas the three-zone distribution in the 31119 active goaf changed only slightly. These results indicate that damage to the retained coal pillar primarily controls the reactivation of oxygen-accessible oxidation conditions in the adjacent goaf. The proposed approach provides a basis for identifying potential spontaneous combustion–prone regions and for targeted leakage sealing, gas monitoring, and fire prevention measures in gob-side entry driving panels.
