Development theory and practice of water injection induced fractures in ultra-low permeability reservoirs

Revealing the impact of core mineral composition on the initiation pressure of waterflood-induced fractures (WIFs) in tight sandstone reservoirs is a crucial aspect of studying the initiation mechanism of WIFs. In this paper, through quantitative characterization of the core mineral composition from six samples of the Chang 6 reservoir in the Wuqi oilfield, western Ordos Basin, and modified experimental cores and displacement equipment for WIF experiments, the influence of the core mineral composition on the initiation pressure of WIFs in tight oil reservoirs is investigated. The conclusions are as follows. (1) The rock mineral composition of the Chang 6 reservoir in the Wuqi oilfield, western Ordos Basin, includes quartz, feldspar calcite, and clay, characterizing it as a typical feldspar sandstone reservoir. Quartz and calcite are considered as brittle minerals, while feldspar and clay are categorized as lithologic minerals. (2) For feldspar sandstone reservoirs, including quartz, feldspar, calcite, and clay minerals, when the combined content of quartz and feldspar exceeds 600% of the total mineral content, the changes of quartz and feldspar content will affect the initiation pressure of WIFs. As the ratio of the quartz content to feldspar content R qf increases, the initiation pressure of WIFs exhibits a logarithmic function decrease. (3) Considering the contribution of diagenetic minerals to rock brittleness, the calculation method for the brittleness index of feldspar tight sandstone reservoirs is improved. (4) The relationships between R qf, brittleness index, and initiation pressure of induced fractures suggest that an increase in R qf leads to a power-law increase in the brittleness index, while the initiation pressure of WIFs relative to the brittleness index shows a power-law decrease. This phenomenon indicates an increased likelihood of WIFs occurring during the long-term water injection process in feldspar sandstone reservoirs. This work contributes to understanding how core minerals affect the initiation pressure of WIFs in tight sandstone reservoirs.

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Influence of Mineral Composition on Initiation Pressure of Waterflood-Induced Fractures in Tight Sandstone Reservoir

Su,

Li,

Bai

et al. 2024

“…Among the analytical models considering the development of natural fractures, the dual-porosity model presented by Warren and Root and the vertical fractured model proposed by Aguilera were the most widely used. , The fluid flow in fractured reservoirs has always been a focal point and a challenge in the field of petroleum engineering. In recent studies, Wang proposed a semianalytical model to describe the bottom-hole pressure behavior of water injectors in fractured reservoirs. , Wei developed analytical models to study the thermal behavior of fractured reservoirs. These studies provide novel approaches to address the fluid flow challenges in fractured oil reservoirs, aiding in the solution of the nonlinear flow equations of FLPGCR …”

Section: Introductionmentioning

confidence: 99%

Semianalytical Modeling for Multiphase Flow in a Fractured Low-Permeability Gas Condensate Reservoir

Yin,

Cheng,

Liu

et al. 2023

Self Cite

During the production of fractured low-permeability gas condensate reservoir (FLPGCR), a phase transition takes place in both the formation and wellbore, resulting in multiphase flow when the pressure drops below the dew point pressure. Additionally, the presence of fractures causes the formation of stress-sensitive characteristics. Nevertheless, traditional analytical models, such as the two-region model or three-region model, overlook the coupling impact of the above factors, which could lead to incorrect pressure transient response and erroneous estimation of well and formation parameters. Therefore, this work presents a semianalytical model for an FLPGCR considering the effects of multiphase flow, stress-sensitive, and wellbore phase redistribution. The gas condensate reservoir is divided into N banks, and the radial fluid saturation variation is modeled by multiple annular reservoirs with a constant saturation in each annular reservoir. The behavior of a fractured reservoir is modeled by using the dualporosity model. The Pedrosa transform was utilized to address the nonlinear differential equation arising from stress-sensitive behavior. To verify the semianalytical solution, it was compared with numerical simulation results from CMG. The results showed that there are 10 flow regimes for the proposed model. The shape of the type curve has the potential to identify the degree of blockage within the FLPGCR. The wellbore phase redistribution only affects the first transitional-flow regime, which slows the rate of pressure drop. The stress sensitivity will lead to the upward characteristic of the curve in a later stage. More attention should be paid to the upward pressure derivative curve at late times, which is conventionally regarded as the effect of a closed boundary when it may not be the case. In addition, the shape factor and composite radius may obscure the radial flow regime. Finally, the proposed model was applied to interpret the pressure measurements recorded from the Bohai field in China, which exhibits a better fitting quality than the traditional models.

“…Water flooding plays an important role in field development; − however, the oil production of many oilfields has declined and entered a high water-cut period in recent years. − To increase the production of high water-cut oilfields while reducing the production cost at a low oil price is an urgent problem. − For example, the PL oilfield in China has many vertical layers and strong heterogeneity. The single-layer water emergence and water content increase rapidly due to the initial joint injection and recovery with large cross-sections.…”

Section: Introductionmentioning

confidence: 99%

Optimization Method of Three-Dimensional Equilibrium Displacement in Thin Interbed Reservoirs

Jiang,

Cheng,

et al. 2023

Self Cite

Most thin interbed reservoirs face a common problem that a nonequilibrium injection and production relationship in plane and vertical directions results in quick water breakthrough, rapid water-cut rise, and a poor water flooding efficiency in a single layer. A finer injection-production strategy should be developed to avoid serious water channeling and an ineffective water cycle. To narrow this gap, this work presents a three-dimensional intelligent equilibrium displacement model (3D-IEDM) to optimize water flooding in thin interbed reservoirs. A water-injection splitting model is first established to determine the water-injection rate of each layer based on displacement pressure and flow resistance. Then, water saturation is calculated for the injection-production well group based on the material balance principle. To achieve three-dimensional equilibrium flooding, the minimum water saturation variance is chosen as the optimization target and the improved particle swarm optimization algorithm is employed to reduce the optimization time caused by iterative calculations. Finally, the 3D-IEDM is programmed as software to provide a quantitative equilibrium flooding optimization scheme in an actual oilfield. The implementation in the pilot B36 well group test of the PL oilfield indicates that the optimization velocity of the 3D-IEDM can optimize the vertical water injection profile of thin interbed reservoirs and improve the sweep efficiency, and the length of time is approximately 14 times less than that of conventional simulator-based methods. Compared with the conventional injection-production scheme, the initial productivity of the pilot well group using the 3D-IEDM increases by 6.45%, and the utilization factor of water injection improves by 15%.