High Permeability Layer Research Articles

Heat Extraction Performance and Optimization for a Doublet-well Geothermal System in Dezhou, China

Dezhou City is located in northwestern Shandong Province, China, and is rich in geothermal resources. Approximately 30% of the geothermal wells and geothermal heating areas of Shandong Province are located in Dezhou. A doublet-well layout geothermal system was completed by the Lubei Geo-engineering Exploration Institute for local winter heating, which has been in operation for 4 years. The wellbores penetrated the Guantao Formation with a well spacing of 180 m. This study aims to assess the heat extraction performance of the current well layout and predict the temperature evolution and lifespan. Furthermore, larger well spacing schemes were used in a simulation to test the heat supply potential and sustainability. In this study, the thermal conductivity and permeability were calibrated using in situ measured data from a field production test. A relatively high permeability layer was found between the depths of 1468 and 1536 m. The temperature remained stable in the first 6 years and then started to decrease. The recharging (injection) water tended to concentrate along the bottom highly permeable layer and accounted for over 64% of the outflow in the 100th year of the simulation test. The outflow temperature decreased from 53.9°C to 50°C in the 32nd year, making it less viable for subsequent sustainable exploitation. Hence, a larger well spacing is required for long-term operation based on the same geothermal reservoir. It was found that a spacing of 400 m could guarantee an outflow temperature above 50°C over a 100-year lifespan with an 80 m3/h pumping (production) rate. Moreover, the sustainability of the 600-m spacing was almost 2.5 times that of the 400 m case. The modeling and analysis method can be useful for the development and optimization of a doublet-well geothermal system under similar conditions.

Heat Flow Correction for the High-Permeability Formation: A Case Study for Xiong’an New Area

Abstract The Xiong’an New Area is located at the western Bohai Bay Basin, 150 km south of Beijing, China. The area has tremendous high heat flow value within the sedimentary layer, and the average value can reach 90 mW·m-2 within the Niutuozhen Uplift. However, combining the basal heat flow at the top of the metamorphic layer with the heat flow value which was contributed by the radiogenic heat production from the overlying formation, the surface heat flow value was only 65.1 mW·m-2 in this area. Thus, the heat flow value within the sedimentary layer was greatly influenced by other factors. In this study, based on the continuous temperature measurements data from 4 boreholes, thermos-physical parameters (conductivity, radioactive heat production, density, and heat capacity) from 90 rock sample measurements, and the regional stratigraphic development, a two-dimensional thermal-hydraulic modelling was carried out to study the influence of the heat refraction and groundwater convection on the heat flow value. According to calculation results, the heat flow disturbance caused by heat refraction was 10 mW·m-2, and the disturbance value was 20 mW·m-2 for the groundwater convection. Furthermore, when the high-permeability layer thickness was a certain value, with the increasing high-permeability layer buried depth, the influence of the groundwater convection on the temperature field which was used for the heat flow calculation became weak. While when the high-permeability layer buried depth was set up, the influence of the groundwater convection on the above temperature field became stronger with the increasing high-permeability layer thickness.

Study on the Water Invasion and Its Effect on the Production from Multilayer Unconsolidated Sandstone Gas Reservoirs

Water invasion is a common occurrence in multilayer unconsolidated gas reservoirs, which results in excessive water production and reduces the economic life of gas wells. However, due to multiple layers, active edge water, and strong heterogeneity, the mechanism of water invasion and its effect in the unconsolidated sandstone gas reservoir require understanding in order to improve efficiency and minimize economic cost. In this study, an experimental study on edge water invasion of the multilayer commingled production in unconsolidated sandstone gas reservoirs was conducted to understand the water invasion process along with different permeability layers. The results show that the edge water invasion in the commingling production is mainly affected by two major factors including reservoir permeability and gas production rate, which jointly control the encroaching water advance path and speed. The nonuniform invade of edge water may occur easily and water prefers to invade toward the gas well along with high permeability layers when the commingling production is in the condition of large permeability gradient and high production rate. The bypass flow will occur when there are high permeability channels between the layers, which causes water blocking to low-permeability layers and periphery reservoirs far away from gas wells. The findings of this study can help for a better understanding of water invasion and the effects of reservoir properties so as to optimize extraction conditions and predict gas productivity in unconsolidated sandstone gas reservoirs.

Migration and plugging characteristics of polymer microsphere and EOR potential in produced-water reinjection of offshore heavy oil reservoirs

Due to the strong heterogeneity, the infaust mobility ratio of offshore heavy oil reservoirs and the high cost of produced water treatment, a “green” in-depth profile control technology was proposed, which integrated produced water reinjection and microsphere in-depth profile control and displacement technology. Experimental results show that RGO-PMSs maintained to be spherical and expanded 5.2–6 time after aging 15 days in brine. While the size of RGO-PMSs aggregation increased 15–25 times, which induced the enhancement of plugging efficiency when permeability was higher than 3000 mD. During RGO-PMSs migration in porous media, it could adjust profile by adsorbing on rock surface or forming plugging in the forms of single capture, bridging, and accumulation. Due to the elastic deformation ability of RGO-PMSs, the particles could enter in-depth reservoirs to form plugging and modulate profile. Moreover, RGO-PMSs system injection and subsequent water flooding could enhance the oil recovery in high permeability layer and low permeability layer of 31.3% and 73.5%, respectively in parallels core displacement experiments. It is believed that the proposed produced water injection combined with RGO-PMSs could be a potential “green” candidate for enhancing oil recovery in offshore heavy oil reservoirs.

ПРИЧИНЫ И АНАЛИЗ ОБВОДНЁННОСТИ ПРОДУКЦИИ НЕКОТОРЫХ МОРСКИХ МЕСТОРОЖДЕНИЙ АЗЕРБАЙДЖАНА

The results of researches of the water encroachment of some offshore fields (Neft Dashlary, Guneshli, Pirallahi, Darwin Banka, Apsheron Banka, Western Apsheron, etc.) of the Republic of Azerbaijan, most of which are at a late stage of development, have been presented. These fields are represented by weakly cemented and loose reservoirs of heterogeneous structure, in which there is an uneven fluid flow. Water breakthrough occurs through high-permeability layers, and layers with low permeability are involved in development to a less extent. Subsequent attempts to involve them in the development process cause an irrational increase in the volume of injected water, which leads to product encroachment. The type of reservoir, characterized by the presence of fracture zones, contributing to the flow of water from the aquifers to the producing wells, as well as improving their hydrodynamic connection with the injection wells, also contributes to the growth of the rate of watering. The geological and technological reasons for the water encroachment have been determined. The heterogeneity of the above mentioned deposits has been proven. It is indicated that an additional reason for the early water encroachment of production wells is the violation of the annulus tightness. Maintaining high rates of oil production is achieved by bringing in new production wells, while most of the watered wells are retired from operation without having exhausted their potential. It is proposed to carry out the measures that will ensure isolation of the most washed out zones and depleted areas of the main productive layer of the field. Methods of selective water isolation and flow diversion technologies should be carried out, first of all, in wells with an increased density of current reserves in order to obtain additional oil production and increase the oil recovery factor, as well as in wells with a high fluid flow rate.

Experimental Investigation of Factors Influencing Remaining Oil Distribution under Water Flooding in a 2-D Visualized Cross-Section Model.

About 70% of the remaining oil remains underground after water flooding, and there is a need to better understand the formation and distribution of this remaining macroscopic oil to enhance oil recovery. In this study, three types of visual plate models were devised with different packing sequences: homogeneous (J), high-permeability layer on top (F), and low-permeability layer on top (Z). Based on these models, several visual flooding experiments were conducted to study the water flooding physics and the remaining oil distribution pattern of an offshore thick heavy oil reservoir under the impact of formation heterogeneity, packing sequence, model length, and permeability contrast during water flooding. These displacements were monitored photographically, and the effluent production profiles were recorded. The results showed that layer permeability and gravitational segregation play an important role during the water flooding process in layered porous media. Experimental results based on the model with different lengths show that the breakthrough oil recovery decreases with the increase of well spacing. Finally, a correction was made to the gravity number by introducing a scaling factor that characterized the formation heterogeneity and packing sequence in thick formation, compared to a known gravity number; the modified gravity number showed a better correlation with breakthrough oil recovery of water and polymer flooding. The research results provide effective guidance for the remaining oil distribution and injection and production parameter optimization in actual reservoirs.

Formation and Performance Evaluation of Colloidal Dispersion Gels Prepared Using Sulfonated Polyacrylamides and Chromium (III) Acetate

Using a sulfonated polyacrylamide (SPAM) and Cr3+, a new colloidal dispersion gel (CDG) was prepared. The viscosity of the CDG samples in different crosslinker concentrations and brine compositions was measured. The results showed that CDGs approach a Newtonian-like behavior in high crosslinker concentrations and salinities, signifying that they possess more rigid, less flexible particles that can be used to block some of the pore throats of the high-permeability layers. Therefore, three core flood tests were performed and the retention of the polymers and the final RRF values (residual resistance factor) were determined. Although CDGs showed a lower tendency to be adsorbed onto the rocks, they caused drastically higher RRF values (caused higher permeability reductions). Thus, it can be concluded that CDGs are superior compared to normal polymer solutions in modifying the permeability. Moreover, changing the post-flood fluid from brine to distilled water caused the RRF to decrease, hence a weaker effect on the permeability.

Experimental investigation of self-gathering microsphere on profile control in heterogeneous reservoir

Profile control in heterogeneous reservoir is an improtant work after water breakthrough. The particle systems have the advantages of less dosage and good controllability compared with the polymers, gelling systems, foams and so on. In order to evaluate the effect of profile control in heterogeneous reservoir, a microsphere system with the self-gathering ability is introduced in this work. The static properties related to the injecting and plugging abilites are also described. The dynamic behaviors during microsphere injection and plugging in porous media are discussed by the homogeneous core experiments, the experimental cores have the permeability ranging from 2.05 mD to 2025.94 mD. The effect of profile control by microsphere injection is analyzed from the heterogeneous core experiment. The results show that the microsphere has the properties of good dispersibility, high thermostability, microdilatancy and self-gathering, which are benefit to the microsphere injectiin and plugging. The analysis of injection pressure, injecting distance and residual resistance factor indicates that the microsphere with the average diameter of 100 nm has the good injecting and plugging abilities in the cores with the permeability ranging from 295.43 mD to 708.41 mD. The microsphere has the good profile control ability in heterogeneous core as it can be retained in high permeability layer, enlarge the sweep volume of subsequent water and improve the oil recovery. The self-gathered microsphere could be an efficient technology for profile control in heterogeneous reservoir.

Weak alkali ASP flooding in the second type reservoir in the A OilfieldProfile control technology and effect

Profile control technology refers to the operation of plugging high permeability layers from injection wells, which can adjust the suction profile of injection layers and improve the ultimate recovery. In this paper, the heterogeneity of the weak alkali ternary compound block of the second kind of oil layer in the A area of the some Second Division is strong, the injection conditions between well groups are different, the injection pressure level of some wells is low, the suction conditions of each sedimentary unit are different, and the comprehensive water cut of the block is high. In order to alleviate the contradiction between in formation and in plane, improve the utilization rate of chemical agents, and improve the ultimate recovery rate of the block, the deep profile control is carried out according to the characteristics of the oil layer development of the well group. Ten profile control wells were selected to adopt the profile control system of one and two polymer gel, which is a water shutoff agent for oil production. The polymer solution was used to carry particles for deep profile control. In this paper, the characteristics of profile control technology and the method of well and layer selection are studied, and the change law of dynamic index after profile control is analyzed in detail.

Seepage Characteristics of Slurry with Particle Additives in the High-Permeability Sand Layer

In the process of the slurry shield construction, the formation of the filter cake is the key to maintain the stability of the excavation face. In high-permeability formation, ordinary pure bentonite slurry is easy to pass through the formation void. Therefore, it is necessary to study the slurry permeability characteristics of the high-permeability sand layer. For the purpose of researching the permeability characteristics of slurry in sandy formation, this paper studies the influence of slurry viscosity on the formation of the filter cake in high-permeability formation under different pressure gradients by the slurry permeability test. The effect of additive particle size on the film-forming gain was studied by adding additives with different particle sizes into pure bentonite slurries with different viscosities. This paper presents a method to determine the optimum slurry viscosity and particle size for high-permeability formation so as to guide the slurry shield construction in high-permeability formation.

Injection-production optimization of carbonate reservoir based on an inter-well connectivity model

Carbonate reservoirs are highly heterogeneous. During waterflooding stage, the channeling phenomenon of displacing fluid in high-permeability layers easily leads to early water breakthrough and high water-cut with low recovery rate. To quantitatively characterize the inter-well connectivity parameters (including conductivity and connected volume), we developed an inter-well connectivity model based on the principle of inter-well connectivity and the geological data and development performance of carbonate reservoirs. Thus, the planar water injection allocation factors and water injection utilization rate of different layers can be obtained. In addition, when the proposed model is integrated with automatic history matching method and production optimization algorithm, the real-time oil and water production can be optimized and predicted. Field application demonstrates that adjusting injection parameters based on the model outputs results in a 1.5% increase in annual oil production, which offers significant guidance for the efficient development of similar oil reservoirs. In this study, the connectivity method was applied to multi-layer real reservoirs for the first time, and the injection and production volume of injection-production wells were repeatedly updated based on multiple iterations of water injection efficiency. The correctness of the method was verified by conceptual calculations and then applied to real reservoirs. So that the oil field can increase production in a short time, and has good application value.

Visual investigation of CO2 dissolution and convection in heterogeneous porous media at reservoir temperature and pressure conditions

AbstractCO2 convective mixing in saline aquifers has been widely studied numerically and experimentally. Reservoir heterogeneity is significant for CO2 convective mixing and experimental studies are still limited. In this study, we have conducted a visualization of CO2 convective mixing experiments in heterogeneous porous media at reservoir conditions using CO2 and water. We have used a two‐dimension Hele–Shaw cell, different glass beads of different permeability at porous media, and water solution with pH indicator. Glass beads were packed in a different way (horizontally and vertically) to generate the heterogeneity inside the test cell. We have studied transport velocity deviation due to the heterogeneity and effects of permeability transition zone together with the effects of boundary conditions. It was found out that having a low permeable layer below a high permeable layer restructure the flow of CO2 fingers and dampens the CO2 transport velocity. With the vertical permeability zones, having a high permeability zone accelerates CO2 gravity transport through that zone which is a good representation for a fracture or a fault in the reservoir. CO2 convection onset is governed by the vertical high‐permeable layer. Boundary conditions have been dominant with the presence of high permeable zones. It also found out that the experimental results presented in this study match with the simulation studies that are available in the literature. © 2021 The Authors. Greenhouse Gases: Science and Technology published by Society of Chemical Industry and John Wiley & Sons Ltd.

Enhanced oil recovery mechanisms of polymer flooding in a heterogeneous oil reservoir

Abstract Taking reservoir rocks and fluids of the Daqing, Dagang and Changqing oilfields as research objects, the EOR mechanisms and technical approach of polymer flooding were discussed. By comparing the displacement performances of ordinary polymer, glycerol, polymer in “sheet-net” structure and heterogeneous weak gel at the same viscosity and concentration, the relationship between the viscosity of polymer displacement agents and displacement performance was demonstrated, and the method of improving polymer flooding effect was worked out. The main mechanism of polymer flooding to increase oil recovery is the swept volume expansion of water injection due to polymer retention in porous media. The viscosity of polymer agents has no positive correlation with polymer flooding effect. Although polymer of “sheet-net” structure has strong capacity in increasing viscosity, it has poor compatibility with pore throat structure of reservoir rock, low injectivity and low shear resistance. Heterogeneous weak gel system has higher adsorption and capture capacity in porous media, which is easy to retain in porous media, and can effectively establish seepage resistance in high permeability layers (zones). Compared with polymer solutions with the same viscosity or concentration, it has stronger ability to expand swept volume. Long term injection of polymer flooding agents will inevitably lead to fluid entry profile reversal, and thus worsening of polymer flooding effect. Alternate injection of high retention and low or non-retention displacement agents can further improve the displacement effect of polymer flooding agents.

Research and application of asynchronous injection-production in ultra-low permeability horizontal well area

When using horizontal wells to exploit ultra-low permeability oil fields, the development effect is usually ensured by increasing the scale of fracturing reconstruction. However, it also leads to the increasing difference of seepage capacity between matrix and fracture, which makes it easier to see water in horizontal wells after water injection and difficult to recover after water cut rises. Therefore, asynchronous injection-production test was carried out in the ultra-low permeability horizontal well area, making full use of the artificial fracture of horizontal well as the high permeability channel, and performing oil-water replacement through full imbibition between high and low permeability layers, so as to improve oil recovery. On the basis of theoretical guidance, during the summary of practice, the main factors affecting the implementation effect of asynchronous injection and production are gradually analyzed, and the reasonable parameters in the implementation process are clearly defined, so as to explore a new treatment method for the middle and high water cut stage in the ultra-low permeability horizontal well area.

Mechanisms on the Injection Conformance Reversion during Polymer Flooding of Offshore Heterogeneous Heavy-Oil Reservoirs

Injection conformance reversion commonly observed during polymer flooding in offshore heterogeneous heavy-oil reservoirs weakens the volumetric sweep of polymer solution and compromises its EOR results. To investigate its mechanisms and impact factors, one mathematical model to predicate injection conformance behavior is constructed for heterogeneous reservoirs based on the Buckley-Leverett function. The different suction capability of each layer to polymer solution results in distinct change law of the flow resistance force, which in turn reacts upon the suction capability and creates dynamic redistribution of injection between layers. Conformance reversion takes place when the variation ratio of flow resistance force of different layers tends to be the same. The peak value and scope of conformance reversion decrease and reversion timing is advanced as oil viscosity or permeability contrast increases, or polymer concentration or relative thickness of low permeable layer decreases, which compromises the ability of polymer flooding to improve the volumetric sweep and lower suction of the low permeable layer. The features of offshore polymer flooding tend to make the injection conformance V-type and create low-efficiency circulation of polymer in a high permeable layer more easily. These results can provide guidance to improve the production performance of polymer flooding in offshore heterogeneous heavy-oil reservoirs.

Numerical simulation of foam diversion acidizing in heterogeneous reservoirs

Abstract Foam diversion acidizing can effectively solve the problem of acid distribution with severe heterogeneity between and within layers. Based on the foam diversion principle, the gas trap theory, and volume conservation principle, the foam slug diversion acidizing model was established and solved considering the change of bottomhole temperature and deviation factor of foam. The simulation results show that the change of temperature has a great influence on the diversion effect at the initial stage of injection, but a small influence at the middle and late stage. The effect of temperature on the highly permeable layer is greater than that of temperature on the low permeability layer. The deviation factor of foam is mainly controlled by temperature at the initial stage, and by pressure at the middle and late stage, and the whole process shows a downward trend, which has little influence on the diversion effect. The quasi-skin factor of gas trap is the most important parameter that influences the effect of foam diversion. The water saturation of the low permeability layer rises faster than that of the high permeability layer, and the effect of diversion is obvious. The research results have a strong guiding significance for foam diversion acidizing.

An investigation on water flooding performance and pattern of porous carbonate reservoirs with bottom water

Water flooding is the most common oil recovery technology for carbonate reservoirs in Middle East. However, because of the various reservoir physical properties, serious problems, such as water breakthrough and uncharted distribution characteristics of remaining oil, bring great challenges to successful water flooding development. In this research, the scaled 3D water flooding experiment with an interlayer heterogeneous and anisotropic physical model was performed to achieve quantitative characterization of water flooding performance and pattern and the distribution of remaining oil after displacement in a porous carbonate reservoir with bottom water. Results indicate that the water flooding performance of bottom water varies with the various permeabilities in different layers. It can be divided into two patterns, characterized by smooth spread in high-permeability layers and coning type breakthrough in low-permeability layers. Specifically, in high-permeability layers, the horizontal flow is faster than vertical flow because the bottom water is mainly controlled by higher horizontal permeability and the lower production pressure difference can't overcome the gravity. Therefore, the whole layer is flooded and there is less remaining oil in high-permeability layers. On the contrary, in low-permeability layers, production pressure difference will drive water to climb up near the vertical wellbore and the water cone appears significantly, resulting in the remaining oil between the wells. In conclusion, the main mechanism behind the water flooding performance can be the heterogeneous and anisotropic characteristics of permeability.

Gradient-Based Production Optimization in Reservoir Development

One of the core contents of intelligent oilfield is to develop proved oil resources economically and effectively. The way to realize it is to make reservoir development in the optimal state in real time based on the existing production conditions. Water flooding is a commonly used technique after primary oil recovery. However, due to the influence of formation heterogeneity, the injected water breaks through the high permeability layer and traps the crude oil untouched. In order to solve such problems, a new optimal control model is proposed here, which aims to maximize the net present value of reservoir development and production. By solving the mathematical model of development and production, the input and output control parameters of reservoir are optimized in real time to obtain the optimal production scheme. This model is based on the reservoir numerical simulation and optimization theory. By solving the gradient of the control variables, multiple objective strategy schemes (such as the optimal one aiming at oil production, water production and economic benefits) can be optimized according to different needs to assist the oilfield production decision. On the basis of theoretical research, this model is used to optimize the calculation and analysis of reservoir examples, and the results show that the optimal production scheme is in line with the actual oilfield, which provides theoretical and technical support for the intelligent control of oilfield development.

Static and flow behaviors of supercritical CO2 foam stabilized with betaine surfactant for mobility control application

Aiming at improving the stability of Supercritical CO2 (SC-CO2) foam in high temperature and salinity reservoirs, a kind of betaine surfactant, Hexadecyl Hydroxypropyl Sulfo Betaine (HHSB), was screened to stabilize SC-CO2 foam. The properties of SC-CO2 foam were improved at elevated temperature and pressure. The effects of surfactant concentration, temperature, pressure and salinity on film drainage rate were measured to explore the stability of SC-CO2 foam. The results showed that an increase of surfactant concentration, pressure and salinity can decrease film drainage rate and enhance the foam stability, which was attributed to the increase of surfactant adsorption at the gas–liquid interface. The performance of SC-CO2 foam formed by HHSB was improved and the tolerant temperature was up to 100 °C. 1-D core flooding experiments indicated that compared with Coinjection of Surfactant and Gas (CSG) method the SC-CO2 foam generated through Surfactant-Alternative-Gas (SAG) method had lower foam strength but better in-depth migration capacity. The high temperature and pressure 3-D sand showed that in Water-Alternative-Gas (WAG) case CO2 broke early through the high permeability layers. In SAG case, SC-CO2 foam can improve the macroscopic sweep efficiency by reducing the CO2 mobility.

Consideration of the Allowable Groundwater Discharge in a Tunnel Project

Ma, J., 2020. Consideration of the allowable groundwater discharge in a tunnel project. In: Hu, C. and Cai, M. (eds.), Geo-informatics and Oceanography. Journal of Coastal Research, Special Issue No. 105, pp. 110–114. Coconut Creek (Florida), ISSN 0749-0208.Alteration to the groundwater flow system during tunneling may be irrecoverable, such as due to excessive discharge-induced groundwater table drawdown and impact to the regional ecological environment. It is therefore necessary and beneficial to specify allowable groundwater discharge during the planning and design of a tunnel project. A case history for a project during which the groundwater was mismanaged in the tunnel design and construction shows the difficulty of coping with the situation in an environmentally and operationally favorable way, especially for sections with a high-permeability belt or layer in the surrounding rocks. To drain groundwater in a controlled mode in a tunnel project, it is vital to specify the allowable discharge in the tunnel design and to control the groundwater drainage magnitude during construction and operation.