Multilateral Horizontal Wells Research Articles

Exploration of production capacity-geomechanical evaluation and CO2 reinjection repair strategy in natural gas hydrate production by multilateral horizontal wells

Multilateral horizontal wells (MHW) can enhance gas production by expanding the natural gas hydrate (NGH) decomposition area, but inevitably leading to larger changes in reservoir pressure and rock stresses, causing subsidence or disasters. Therefore, this study established a THMC model that evaluated the production effect and geomechanical response of MHW in Class-I reservoirs with different permeability and proposed a CO2 reinjection repair strategy to achieve subsidence recovery and carbon storage. Results indicate that MHW with vertical branch arrangements performs best in short-term production for low-permeability reservoirs, while the temperature and pressure evolution in high-permeability reservoirs is more drastic than in low-permeability reservoirs, producing many unfavorable factors. Higher capacity also results in larger strata subsidence and stress changes, affecting the reservoir stability and wellbore safety: (i) subsidence occurs mainly in the NGH sediment and the upper zone of the wellbore; (ii) normal stresses around the wellbore increase most significantly in the vertical direction, while shear stresses generally decrease. The repair indicators of subsidence recovery rate, energy recovery rate, and hydrate conversion rate suggest that reinjecting CO2 into depleted NGH reservoirs can improve the mechanical properties of the strata and achieve carbon storage via the hydrate method as well.

In situ coal permeability and favorable development methods for coalbed methane (CBM) extraction in China: From real data

Permeability plays a significant role in the economic viability of coalbed methane (CBM) development. In China, in situ permeability obtained from injection fall-off tests range from 0.0001 to 41 mD at depths of 130–1728 m, with the majority (78%) falling between 0.01 and 1 mD. Coal reservoirs with high rank, common cleat mineralization, and depth-dependent high stress may result in extremely low permeability. Low-rank coal and cataclastic coal exhibit more favorable permeability conditions at shallow depths. Heterogeneity in coal rank, coal texture, and stress magnitude results in a discrete distribution of permeability both regionally and vertically. Most deep seams are highly compressed with extremely low permeability (<0.1 mD) as high stress levels. Multilateral horizontal wells work best with high permeability seams, while vertical wells with conventional hydraulic fracturing demonstrate limited adaptability to deep and low-permeability seams due to insufficient proppant-supported fractures. With increasing depth, both vertical and horizontal wells should employ larger fracturing scales to create effectively supported zones with higher fracture conductivity and reduced stress sensitivity to enhance CBM productivity. Horizontal wells with large-scale volume fracturing demonstrate superior performance compared to vertical wells in extracting CBM from deep, low-permeability, and high gas saturation reservoirs.

Parametric study of the geothermal exploitation performance from a HDR reservoir through multilateral horizontal wells: The Qiabuqia geothermal area, Gonghe Basin

Parametric study of the geothermal exploitation performance from a HDR reservoir through multilateral horizontal wells: The Qiabuqia geothermal area, Gonghe Basin

Enhancement of gas production from hydrate reservoir using a novel deployment of multilateral horizontal well

Most marine hydrates deposit in low permeable argillaceous sediments. However, the gas production rate of current field trials for hydrate reservoir is lower than the commercial criterion. To enhance gas production, a novel multilateral horizontal well was numerically investigated based on an unconfined hydrate reservoir in the Shenhu Area in the South China Sea. The investigation shows the novel deployment enhances gas production rate due to the enlarged dissociation region and a great quantity of stimulated hydrates. The release rate of gas from hydrate exceeds the production rate, 70% of produced gas is gaseous methane and water-to-gas ratio is favorable. For various factors, increasing the length and the number of lateral well significantly enhances the gas and water production rates, which raises about 30% with additional 100 m lateral well. The lateral well deployed in the middle of reservoir causes a high gas rate and low water rate, and the angle of the main and lateral wellbores (ANGMW&LW) slightly affects the gas production. The sequence of factor of the deployment on gas production herein is: well length, depth, spacing, ANGMW&LW. The commercial gas rate could be achieved with 22 groups of 1000 m length multilateral well.

Multi-lateral horizontal well with dual-tubing system to improve CO2 storage security and reduce CCS cost

This paper proposes a multi-lateral horizontal well with a dual-tubing (MLHW-DT) system to improve CO2 storage security and reduce the cost of carbon capture and storage (CCS) at a saline aquifer. In CCS, the production and re-injection of brine are efficient methods of relieving overpressure and improving the CO2 storage security simultaneously. In our previous study, a horizontal well with a dual-tubing (HW-DT) system operating on an onshore platform reduced CCS cost. In this study, the proposed MLHW-DT system is designed to implement the concept of the re-injection of produced brine to improve CO2 storage security while supplementing the shortcomings of the conventional brine production system by reducing CCS cost. When we vary the vertical-horizontal permeability ratio and dip angle of a saline aquifer, the CO2 storage security of the MLHW-DT system is improved compared with that of the overall HW-DT system because the re-injected brine induces the CO2 plume migration in the lateral direction. Furthermore, the CCS cost of the MLHW-DT system is reduced by 69.4% compared with that of the conventional brine production system if the MLHW is operated on an onshore platform. Based on these results, the MLHW-DT is a safe and economical operation system for a CCS project.

Assisted history matching and graphical methods for estimating individual layer properties from well testing data in stratified reservoirs with multilateral wells

One of the main purposes for conducting well tests is to obtain information about reservoir parameters, such as its permeability and the existence of skin effects. Determining individual layer properties from pressure transient data in multilayer reservoirs is challenging, since pressure behavior is influenced by the properties of all layers. This work presents three methods for estimating layer properties from well testing data in multilayer reservoirs with multilateral wells. First, we extend two existing graphical straight-line methods for estimating individual layer properties in multilayer systems with vertical wells to stratified reservoirs with multilateral horizontal wells. These techniques are the rate-normalized pressure analysis and the delta transient method. Both methods require a clear identification of radial flow regimes, which may not occur in a practical case. Additionally, we show that a computer-assisted history matching method based on the Nelder–Mead optimization algorithm can also be used to evaluate layer permeabilities and skin. This optimization method does not rely on the identification of any specific flow regime. Estimates obtained from the graphical methods were used as initial guess for the assisted history matching. The proposed techniques are applied on a set of synthetic well-test cases, where pressure and layer flow-rate profiles are computed from an existing analytical model. Results show that all three methods are able to yield good estimates for layer properties if both early- and late-time radial flow are observed. In cases where only one of the radial flow regimes is identified, then the NM algorithm provides the best results, showing that the assisted history matching improved the estimates provided by the graphical method.

Heat extraction study of a novel hydrothermal open-loop geothermal system in a multi-lateral horizontal well

The efficient development of hydrothermal resource is an important focus in the global geothermal industry. A novel hydrothermal open-loop geothermal system in a multi-lateral horizontal well is presented to achieve the simultaneous exploitation of multi-layer reservoirs and accelerate the large-scale development of the hydrothermal resource. To investigate the detailed performance of the novel geothermal system, a novel 3D fluid flow and heat transfer numerical model is established based on the local thermal non-equilibrium and dual porosity theories. The flow and temperature fields are analyzed, while the pressure and temperature interferences between the lateral wellbores of the multi-lateral horizontal well system are comprehensively investigated. The influences of the injection flow rate, lateral-wellbore number, spacing between the injection segment and the main wellbore, fracture aperture on the heat extraction are studied. Furthermore, the thermal characteristics of the novel geothermal system and traditional doublet well system are compared for the first time. The investigation indicates that the flow impedance of the novel geothermal system can decrease by 75.38%, and its energy efficiency reaches 8 times that of the doublet well system. The findings can provide a key reference for scientific research and application of the novel and traditional geothermal systems.

Recommendations for the multilateral wells design selection in various geological conditions based on lessons learned

The authors of the article have summarized the experience of multilateral well application, performed an efficiency analysis of multilateral wells vs horizontal wells in Rosneft Oil Company's fields with various subsurface architecture. The algorithm for multilateral well efficiency estimation, compared to other type of well completions, was developed. This algorithm is based on the selection of areas for well locations with similar reservoir properties, reservoir energy conditions, and reservoir development conditions to evaluate production startup parameters, decline rates, cumulative parameters for the areas of over 6 month production. A matrix of multilateral well applicability in various geological conditions was generated, and recommendations for preferable well design were made. This type of analysis was conducted for the first time due to collection of sufficient statistical data, because of a multiple increase in the amount of drilling complex wells in the recent years. The obtained results provide an opportunity to design an efficient field development system for new assets, perform an adjustment of brownfields development systems, select multilateral well design for certain geological conditions based on lessons learned.

Application of drilling of multilateral well on the basis of new technology and model in south Caspian basin

The article discusses the issue of drilling multilateral horizontal wells and provides a brief history of its development. Data were provided on the selection of the location of the multilateral horizontal well, drilling the main wellbore and determining the depth for running the сasing strings. This paper also analyzes the selection of lateral wellbore penetration depth, the importance of drilling multilateral horizontal wells and their application for the first time in the shelf water of South Caspian Basin, at the Western Absheron field, Well 19. Keywords: multilateral wells; drilling of horizontal wells; petrophysical models; drilling of main and lateral wellbores.

Completion, development and prospects of multilateral wells

The paper reviews the completion and development of multilateral horizontal wells. Brief data on location schemes of multilateral horizontal wells and completion levels is presented as well. At the same time, the paper analyzes the significance of drilling multilateral horizontal wells in the modern experience of oil and gas production, and their first implementation on the shore of South Caspian in the well No 19 of Garbi Absheron field.

Numerical study of gas production from fine-grained hydrate reservoirs using a multilateral horizontal well system

Natural gas hydrate is prevalent in ultralow-permeability fine-grained sediments with substantial reserves. However, effective and safe gas production from fine-grained hydrate reservoirs remains a global challenge. Here, a multilateral horizontal well system is innovatively employed to improve production efficiency in fine-grained hydrate reservoirs. A three-dimensional (3D) numerical model of a real gas hydrate reservoir is constructed, and the influences of well configuration, deployment location, depressurization pressure, and reservoir properties on production are systemically and quantitatively evaluated. The spatial distributions of the physical properties of the 3D reservoirs during gas production are clearly revealed. The results indicate that the production efficiency of multilateral horizontal wells improves with increasing branch number and length, particularly when the ratio of branch length to reservoir width exceeds 0.15. Branch interference and perforation length positively affect production enhancement when multilateral horizontal wells are deployed in hydrate reservoirs with specific ultralow permeabilities; these discoveries are revealed for the first time. Multilateral horizontal wells with helically and vertically distributed equal-length branches yield high production efficiencies, and their optimal locations are in the lower sections of the reservoirs, particularly within high-isotropic-permeability reservoirs. Moreover, uniformly low depressurization pressure in helically distributed branches facilitates gas extraction; gas recovery efficiency increases by 8% when production pressure decreases by 1 MPa. This study suggests that the use of a helical multilateral well system is a promising strategy for achieving commercial gas production from fine-grained hydrate reservoirs.

Reservoir and Wellbore Flow Coupling Model for Fishbone Multilateral Wells in Bottom Water Drive Reservoirs

AbstractNowadays, different types of complex production wells are applied in challenging reservoirs in order to maximize oil recovery. A representative application is the fishbone multilateral horizontal wells, which have advantages of expanding the drainage area information and reducing the pressure loss in the long single lateral wellbore. This paper investigated the performance of fishbone wells and derived a wellbore and reservoir flow coupling model for fishbone multilateral wells in the bottom water reservoirs. The new model considered plenty of parameters that may have significant impacts on productivity and pressure drop in the well, including the fishbone structure, the main and branch wellbores’ length, the spacing distance of the branch wellbores, wellbore radius, and preformation parameters. Furthermore, a sensitivity analysis example by the numerical method is presented in this paper. Compared with other models, our coupling model, when it is degraded to horizontal well, is more consistent with the results of actual field situation. In another comparative analysis, the results of the new model with branches show a good match with the numerical simulation results by software. The proposed method in this paper can be used as a valuable tool to analyze the productivity, wellbore inflow profile, and pressure profile of the fishbone multilateral wells in the bottom water reservoir.

Analytical solutions for injectivity and falloff tests in stratified reservoirs with multilateral horizontal wells

The availability of analytical solutions to analyze injectivity and falloff tests is desired to estimate well injectivity performance and reservoir parameters owing to their simplicity in interpreting pressure transient data acquired during such tests. However, the currently available analytical solutions can only describe injectivity and falloff tests in single-layer reservoirs with horizontal wells and multilayer systems with vertical wells. Therefore, the main purpose of this work is to develop new analytical solutions that can be used to accurately interpret and analyze injectivity and falloff tests conducted in multilayer reservoirs drilled by multilateral horizontal wells under two-phase flow. The presented solutions showed a good agreement with the results obtained from a general purpose commercial reservoir simulator. Moreover, the proposed solutions can be used to accurately estimate the reservoir equivalent permeability and also as forward models for nonlinear regression techniques and history matching methods.

A Semianalytical Coupling Model between Reservoir and Horizontal Well with Different Well Completions

Although currently, large-scale and multilateral horizontal wells are an important way to improve the oil recovery in the unconventional reservoirs, the flow behavior of fluid from the reservoir into the horizontal wellbore becomes more challenged compared to the single small-scale horizontal well. One of the main challenges is that pressure loss from the well completion section and wellbore cannot be ignored in the coupling process between the reservoir and the horizontal well. In this paper, a new method is presented to solve the coupling flow between the reservoir and the horizontal well with different well completions. The new coupling model is compared with Ouyang’s model (1998) and Penmatcha’s model (1997), and the predicted data are consistent with each other at both early and late times. Meanwhile, four different cases have been proposed to verify the application of the new coupling model with different well completions, and the results indicate that the uneven inflow profile can be effectively alleviated via reasonable completion parameters and different well completions. Based on two types of flow-node units, it can quickly model and solve the coupling problem between the reservoir and the horizontal well with complex completion cases. It can also depict the inflow profile of the horizontal well with different well completions, which is conducive to understand the coupling process. The new coupling model can provide theoretical support for further optimization of completion parameters and well completions and finally improve oil recovery.

Semi-analytical modeling of pressure-transient response of multilateral horizontal well with pressure drop along wellbore

The primary purpose of this work is to develop a generalized model to rigorously account for the pressure drop within multilateral horizontal well (MLHW) with any number of laterals in arbitrary configurations. The finite-conductivity wellbore model ranging from laminar to turbulent-flow regimes is implemented to incorporate a three-dimensional flow in the reservoir. Reservoir inflow for entire time period is handled by integrating the instantaneous Green's function over space in the Laplace-transformed domain. A semi-analytical approach using the dimension-transform technique is proposed to solve the coupled reservoir-wellbore model, which is then verified against alternative results. On the basis of solutions, the transient responses are investigated in terms of wellbore pressure, pressure derivative, and pressure/flux profiles along laterals. Two common patterns (i.e., radial-clustered and pinnate-branched MLHWs) are proposed to investigate transient pressure responses. The results demonstrate that the pressure-transient behaviors depend on the interaction between wellbore hydraulics, Reynolds number, and MLHW configuration. This work provided some insights into better understanding the differences and similarities between a finite-conductivity single-lateral and multi-lateral systems.

A transient flow model for multilateral horizontal wells in bottom water drive reservoirs

The aim of this paper is to describe the pressure dynamic behaviour around a multilateral horizontal well in bottom water reservoir and get the productivity by establishing an analytical transient flow model. An exact solution of the model is derived by means of orthogonal transformation, method of mirror images and the theory of potential superimposition. For bottom water reservoirs, there is a supplementary boundary for the water aquifer. Given enough time, the transient flow will change to steady flow gradually. Correspondingly, the productivity index for wells in bottom water drive reservoirs can be calculated. We conclude that the analytical solution to the model can provide a valuable tool to compute the productivity and pressure dynamic behaviour of the multilateral horizontal wells in the bottom water reservoirs. Moreover, the case study shows that the calculated results agree with the practical situation. [Received: August 12, 2017; Accepted: March 16,2018]

Study on Production Decline Law of Multilateral Horizontal Well in Coalbed Methane Reservoirs

China is rich in coal-bed gas resources, however, because of the low abundance of coalbed methane, the low filtration ability of coal matrix and the complexity of gas streaming process, causing the single well productivity of conventional coalbed methane well is low. To improve the individual well producing rate and the economic effects of coal-bed gas reservoirs, the multilateral horizontal wells are being popularized on a large scale. Therefore, it is necessary to study the production decline law of multi-branch horizontal well in coalbed methane reservoirs. Based on the seepage physical model, a mathematical model based on resolution-diffusion-filtration was established. By using the point source function, the bottom pressure response function of single branch horizontal well was solved. By utilizing the theory of pressure superposition, mathematical model of production decline was gained, and the key elements influencing production decline were analyzed. The research results in this paper will have some guiding significance for efficient development of coalbed methane.

A high-efficiency development mode of shale gas reservoirs in mountainous areas based on large cluster horizontal well engineering

With the basic characteristics of conventional horizontal wells, the so-called complex wells including horizontal extended-reach wells, multi-lateral horizontal wells, U-shaped wells, cluster horizontal wells, etc., are advanced well types for the efficient development of low-permeability, unconventional, deep-water, and deep oil and gas reservoirs, which have been highly concerned all over the world. Significant progress at home and abroad has been made in relevant researches and practices and is expected to play an important role in the efficient development of shale oil and gas. To meet the basic needs of environment & safety, land conservation, cost reducing and efficiency improving, it is urgent to create a unique and efficient mode for developing shale gas. Therefore, an efficient shale gas development mode for mountainous areas and an engineering and technical support system are presented based on large cluster horizontal-well engineering. An equation is thus obtained for calculating the maximum number of horizontal wells arranged allowably in “Well Factory” on a single platform. The general research and development of large extended-reach well technology are analyzed by expounding the basic concept of an extended-reach well and its drilling extension limit. And a calculation method is thus established to predict the maximum measured depth of open hole in extended-reach drilling. Moreover, some relevant research results and their significance for downhole tubular mechanics & mechanical extension limits in extended-reach drilling are also briefly introduced in this paper. The conclusions are drawn that, by following the idea of “integration of geology and engineering” in oil and gas development, these research results have a foreseeable application prospect in shale gas development in the mountainous areas in the future, and will contribute to new progress in China's “Shale Revolution”.

A coupling model of water breakthrough time for a multilateral horizontal well in a bottom water-drive reservoir

A series of complex production wells have been applied in challenging reservoirs to maximize oil recovery. Multilateral horizontal well has received plentiful attentions in recent years. The multilateral horizontal well technology is especially beneficial in expanding formation drainage area, reducing water cresting and coning, increasing productivity, and postponing water breakthrough time in bottom water reservoir. Since Muskat and Wyckoff introduced the concept of water coning into petroleum engineering field, different models have been proposed to forecast the critical rate and water breakthrough time for vertical and horizontal wells. However, the studies of water breakthrough time for complex structured multilateral horizontal wells have rarely been reported. This paper proposes a new coupling model for estimating the water breakthrough time of complex structured multilateral horizontal wells. The proposed model took multiple factors into account, including the wellbore 3D structure, wellbore vertical location, and reservoir and fluids properties. In addition, a field case study was conducted by utilizing the methods that were proposed in this paper. The practical production data was compared with the results obtained from the analytical model, and this coupling model shows an excellent agreement with the results from the actual scenarios. The proposed methods in this paper can be utilized to forecast the water breakthrough time and breakthrough locations of multilateral wells in bottom water reservoirs.

Fishbone type horizontal wellbore completion: A study for pressure behavior, flow regimes, and productivity index

This paper focuses on studying pressure behavior, flow regimes, and productivity index of oil and gas reservoirs depleted by horizontal wells with a fishbone type completion technology. The main objective is introducing an integrated approach for the favorable configuration and distribution of multilateral horizontal wells extending in porous media at arbitrary directions and arbitrary permeability trajectories. The study aims to demonstrate the advantages and disadvantages of fishbone completion in terms of transient and pseudo-steady state productivity index considering single phase flow in the porous media. It is also an attempt to propose new analytical models for the expected flow regimes and new practical solutions for estimating stabilized productivity index for different scenarios of fishbone completion.In this study, pressure distribution in the porous media is described by several analytical models considering different reservoir geometries and different multilateral horizontal wellbore configurations. These models are solved for single and dual porous media where naturally induced fractures exist. Lateral and spatial permeability are considered in these models as well as non-Darcy flow impact close to the vicinity of the wellbores in gas reservoirs. The solutions of these models are used to generate analytical models for the flow regimes that can be observed during the entire production life. Transient and stabilized productivity indices are quantified for the case of constant production rate using the observed pressure responses of fishbone type horizontal wells. The starting time of pseudo-steady state and the stabilized pseudo-steady state productivity index are used to assess the optimal configuration for fishbone completion.The observations are summarized in: 1) Pressure behavior, flow regimes, and productivity index of fishbone type horizontal wells are impacted by main wellbore and laterals distribution, however, laterals distribution in both sides of the main wellbore may not have an impact in isotropic formations. 2) Azimuth and vertical deviation angles from the main horizontal wellbore and lateral and spatial anisotropies have similar impacts because they change hypothetically the lateral length. 3) The impact of azimuth angle might be maximized by the lateral anisotropy while spatial anisotropy could maximize the impact of vertical deviation angle. 4) The conjunction points of the laterals and the main wellbore may not have a significant impact. 5) Productivity indices of fishbone type horizontal wellbores during early and late production times are less than the ones obtained by single horizontal well, however, almost identical indices are seen at intermediate production time when linear flow regime is observed. 6) The starting time of pseudo-steady state flow is controlled by the main wellbore length more than the laterals’ characteristics unless these laterals extend to reservoir boundaries.The conclusions summed up from the results of this study are: 1) Eventhough fishbone type completion could be significant solution for a lot of operation problems of long horizontal wellbore such as excessive pressure drop and wellbore instability, it is not necessary delivering optimum reservoir performance. 2) Flow regimes and flow patterns (transient or pseudo-steady state) are affected by the characteristics and distributions of the main wellbore and laterals in the porous media.