Multilateral Horizontal Wells Research Articles

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.

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]

MULTI-LATERAL WELLS DRILLING USING RAPID TECHNOLOGY

The article deals with the issues associated with drilling multi-lateral horizontal wells. A short history of development of multi-lateral drilling is presented. The history of the development of the Technology Advancement - Multi-Laterals (TAML) classification, which was initiated by Eric Diggin at the International Forum «Technology Advancement - Multi- Laterals» in March 1997, is presented. The classification of TAML complexity levels is presented, which includes six levels. The distinctive features of each of the six levels of drilling complexity of multi-lateral wells are given. The article gives a brief description of the development of multi-lateral drilling technology. Data on the first drilled wells corresponding to different levels of complexity are given. There described the reliability and strength of the articulation of the RAPID brand. The advantages of the Rapid Tie Back, Rapid Access, Rapid Connect, Rapid Exclude and Rapid X joints are discussed and described. A distinctive feature of the Rapid Tie Back joint is the availability of factory-made cutouts in the casing. When using the Rapid Access joint, it is planned to cut the oriented side windows in the casing when mounting joints with lateral trunks using a branch pipe with a special groove. The junctions of the Rapid Connect and Rapid Exclude grades allow selective entry into the main and side trunks. The articulation of the brand Rapid X is distinguished by the presence of a continuous fixing rail. The design requirements and application specifics are given. The advantages of using the Rapid X junction are described. The article presents typical designs of multi-hole wells. The authors' design of a multihole well is also presented, the construction of which provides for the use of the Rapid X connector. The advantages of multi-lateral drilling are considered.

Geomechanical optimization of hydraulic fracturing in unconventional reservoirs: a semi-analytical approach

Unconventional drilling and completion architecture includes drilling multilateral horizontal wells in the direction of minimum horizontal stress and simultaneous multistage fracturing treatments perpendicular to the wellbore. This drilling and stimulation strategy is utilized in order to raise the connectivity of the reservoir to the wellbore, thereby remedying the low permeability problem, increasing reserve per well, enhancing well productivity, and improving project economics in this type of reservoir. However, in order to have the highest production with the least cost, an optimization technique should be used for the fracturing treatment. According to the fact that aperture, propagation direction, and propagation potential of hydraulic fractures are of paramount importance in optimization of the fracking treatment, in this research paper, these three major factors are studied in detail, the control variables on these three factors are examined, and the effect of each factor is quantified by proposing a complete set of equations. Using the proposed set of equations, one can make a good estimate about the fracture aperture (directly controlling the fracture conductivity), the stress shadow size (directly controlling the fracture path), and the change of stress intensity factor (directly controlling the fracture propagation potential). A geomechanical optimization procedure is then presented for toughness-dominated and viscosity-dominated regimes based on the proposed equations that can be used for estimation of different optimal fracturing patterns. The most efficient fracturing pattern can be determined afterward via considering the cumulative production using a reservoir simulator e.g. ECLIPSE, Schlumberger. This procedure is likely to offer an optimal simultaneous multistage hydraulic fracture treatment without deviation or collapse, with no fracture trapping, with the highest possible propagation potential in the hydrocarbon producing shale layer, and a predicted aperture for proppant type/size decision and conductivity of the fractures.

Engineering geological models for efficient development of high-rank coalbed methane and their application – Taking the Qinshui Basin for example

Low average single-well production resulting in low economic benefit has become the main bottleneck of the CBM gas development in China. So it is significant to choose suitable efficient development technologies based on CBM geological factors for high rank CBM recovery enhancement. In view of this, CBM geological factors were analyzed, different geological models were established and the corresponding models of development engineering technologies were thus put forward. It was proposed that the four main factors affecting high rank CBM recovery from a lower degree to a higher degree respectively include coal texture, rank of coal metamorphism, in-situ stress, and the ratio of critical desorption pressure to initial reservoir pressure. On this basis, four engineering geological models were classified as follows: vertical well, open-hole multilateral horizontal well, U-shaped and roof tree-like horizontal wells, and fish-bone and L-shaped wells. It is concluded that the former two models are more adaptable in such areas with better coal texture and high degree of thermal maturity, while the latter two are commonly applied in a wide range of areas.

Deep insights to transient pressure behavior and stabilized productivity index of multilateral wells in laterally and spatially anisotropic reservoirs

The objective of this paper is focusing deep insights on stabilized productivity index (PI) and transient pressure behaviors and flow regimes of multilateral wells. It introduces an integrated approach for the performance of reservoirs depleted by multilateral wells extending in arbitrary trajectories. The study introduces new practical solutions for estimating stabilized pseudo-steady state (PSS) productivity index and starting time of PSS as well as transient PI behavior of multilateral wells in single and dual porous media with laterally and spatially anisotropic characteristics.Several analytical models are used in this study for describing pressure and pressure derivative behavior of multilateral wells considering different reservoir configurations and types and different wellbore lengths and directions. These models are developed for laterally and spatially anisotropic reservoirs consisting of single homogenous and dual heterogeneous porous media (Naturally fractured reservoirs) and depleted by multilateral wells extending from single vertical wellbore at different horizons and directions. The models are modified to identify the staring time of PSS flow or the time when boundary dominated flow regime is developed. They are also applied to estimate the time variant transient PI and time invariant stabilized PSS PI for constant single lateral flow rate or constant vertical wellbore commingled flow rate.The outcomes of this study are summarized in: 1) Developing new analytical solutions for pressure distribution in porous media drained by multilateral wells. 2) Developing new integrated approach for estimating stabilized PSS productivity index. 3) Understanding pressure, pressure derivative, and PI behavior of finite acting reservoir depleted by multilateral horizontal wells during transient and PSS production. 4) Investigating the impacts of different reservoir configurations and types, wellbore lengths and directions, permeability anisotropy characteristics, and single and dual porous media petrophysical properties on stabilized PSS productivity index.The novel points in this study are: 1) The optimum reservoir configuration that gives the maximum stabilized PI is the rectangular shape reservoir with reservoir length to width ratio of (2−4). 2) The lateral with long wellbore and the slightly deviated from the horizontal directions gives the greatest stabilized productivity index. Stabilized PI is impacted by the length and direction of each multilateral as well as lateral wellbore location in the vertical plane. 3) Lateral reservoir anisotropy exhibits bad PI compared to the spatial anisotropy. 4) PI of conventional dual porous media reservoirs is greater than the index of unconventional reservoirs at early and late production time, but the index at intermediate production time demonstrates the greater value for unconventional reservoirs.

Coalbed methane recovery from multilateral horizontal wells in Southern Qinshui Basin

Since 2006, more than 80 multilateral horizontal wells have been drilled in Panzhuang block, Southern Qinshui Basin. In this paper, 6 typical wells in a region are selected as an example. The thickness of coal, gas content, reservoir pressure, permeability, burial depth, and reservoir pressure conditions are analyzed. The practice shows that production by multilateral horizontal well declines from 43,111 m 3 /day per well in the 2nd year to 25,126 m 3 /day per well in the 4th year. The numerical simulation result shows that the lateral interference forms in Well QNP05 after two years of gas production, and the gas content is reduced to less than 8 m 3 /t within the controlled region after six years. The area of gas content was less than 8 m 3 /t after eight years of gas production is about 3.2 km 2 , which is about 76% of the controlled area of the six multilateral horizontal wells. The results indicate that multilateral horizontal wells contribute to high production rates at potentially profitable levels and can also serve as an effective tool for a high-rank CBM field drainage. Cited as : Liu, S., Tang, S., Yin, S. Coalbed methane recovery from multilateral horizontal wells in Southern Qinshui Basin. Advances in Geo-Energy Research, 2018, 2(1): 34-42, doi: 10.26804/ager.2018.01.03

Coalbed methane recovery from multilateral horizontal wells in Southern Qinshui Basin

Coalbed methane recovery from multilateral horizontal wells in Southern Qinshui Basin

Problems in the development of high-rank CBM horizontal wells in the Fanzhuang–Zhengzhuang Block in the Qinshui Basin and countermeasures

Coal reservoirs in the Qinshui Basin are characterized by high thermal evolution degree, low permeability, low reservoir pressure, lower gas saturation and strong heterogeneity, so its coalbed methane (CBM) development is quite difficult. In this paper, the development practice of high-rank CBM horizontal wells in the Fanzhuang–Zhengzhuang Block was analyzed in terms of geological and engineering factors to clarify the productivity influencing factors, suitable geological conditions and potential tapping countermeasures of multi-lateral horizontal wells. It is shown that the reasons for the low development efficiency of multi-lateral horizontal wells are divided into three types. The first one is geological factor, such as encountering low CBM content areas or faults. The second is engineering factor, such as drilling fluid plugging, drilling collapse, drainage collapse and dust coal blockage. The third is the combination of both factors. It is concluded that encountering low CBM content areas and faults, collapse and blockage are the main reasons for the low production of multi-lateral horizontal wells in the Zhengzhuang–Fanzhuang Block, with the CBM content higher than 20 m3/t, the ratio of critical desorption pressure and reservoir pressure higher than 0.7 and vitrinite reflectance (Ro) higher than 3.8. The prerequisite for an open-hole horizontal well in this area to produce CBM at a high rate is that the well lies in the tensile stress zone. Finally, the countermeasures to tap the potential of some inefficient wells were put forward. First, the inefficient wells which are blocked with dust coal or collapsed in the later stage should be stimulated based on classifications. And second, it is necessary to explore new types of horizontal wells so as to deal with borehole collapse and continue the operation in the later stage by using tree-like roof horizontal wells, single-lateral horizontal wells with casing or screen completion and fish-bone horizontal wells.

Numerical simulation of MZF design with non-planar hydraulic fracturing from multi-lateral horizontal wells

In recent years, developments in the oil and gas industry have evolved significantly in advancing the mechanical systems technology to perform hydraulic fracturing. However, further developments will require an in-depth understanding of the impacts of fracture spacing, stress anisotropy, and reservoir characterization. In order to develop a comprehensive and robust completion design for hydraulic fracturing from multi-lateral wellbores with closely spaced fractures, it is important to consider stress shadowing effects. In this work the Cohesive Segments Method is combined with the Phantom Node Method, a combination termed CPNM. This is capable of not only simulating non-planar hydraulic fracture propagation with an unpredictable path, but also simulating the emergence of multiple cohesive cracks within a porous medium. This paper focuses on the “Modified Zipper-Frac” (MZF) design, which has been introduced to design the clusters from multi-lateral wells with the aim of increasing the fracture complexity. Validation of the numerical technique has been performed by comparing the solution for an individual hydraulic fracture with a Khristianovic-Geertsma-de Klerk (KGD) solution. In addition, a study of the development of double fractures has been conducted in the presence of stress shadowing to verify the simulation results. Taking the stress shadowing effects into account, a large number of numerical simulations are conducted using CPNM to investigate the stress anisotropy as well as the in-plane shear stress in the area between the two wells. The main contribution of this work is the detailed investigation of the effects of stress shadowing as a function of the fracture spacing on the horizontal stress contrast, direction of maximum local stress, leak-off flow rate, in-plane shear stress, and pore pressure of the formation.

Prediction of Coal Bed Methane Recovery Rate and Its Improvement Measures in Dafosi Mine Field

The recovery rate of coalbed methane (CBM) can reflect the mining situation and the residual gas in coal reservoir. It plays an important role in the calculation of the recoverable resources. This paper mainly uses isothermal adsorption curve method and hydraulic model method to predict recovery rate of CBM. The isothermal adsorption curve method considering desorption lag problem in the prediction process, which is more in line with the actual situation. In the hydraulic model method, the recovery rate of “V” type well is the largest in the early stage. But with the time going on, the recovery rate of multilateral horizontal well is greater than vertical well, “U” type well and “V” type well finally. The factors affecting CBM recovery rate include geological characteristics, development conditions and economic factors. The geological characteristics of coal reservoir are the main factors affecting CBM recovery rate, and corresponding measures can be adopted to improve the recovery rate.

A semi-analytical model for multilateral horizontal wells in low-permeability naturally fractured reservoirs

Multilateral horizontal wells (MLHWs) can significantly increase the reservoir exposure as well as connect high-permeability areas (natural fractures), and thus have been widely adopted in petroleum industry as an effective technique for efficient development of low-permeability reservoirs. Compared to vertical wells and horizontal wells, the flowing problems caused by MLHWs are more complex. In addition, extensive study has revealed that stress sensitivity of permeability in low-permeability reservoirs is obvious which cannot be ignored, especially for naturally fractured dual-porosity reservoirs. The non-linearity caused by stress sensitivity of permeability further complicates the flowing problems of MLHWs; however, so far, little work has been done in literature to simulate pressure transient dynamics of MLHWs with consideration of stress-sensitivity effect of permeability in low-permeability reservoirs.In this paper, a more rigorous analytical model for MLHWs in low-permeability naturally fractured reservoirs is presented. The model can not only consider different combinations of multiple branches, it can also consider the stress-sensitivity effect of reservoir permeability. The non-linear mathematical model can be linearized by Pedrosa transform and perturbation technique, and the final solution thus can be obtained by Laplace transformation method, finite cosine transform, element discretization and matrix theory. The presented model and corresponding solution are first validated by comparison with transient pressure responses calculated with a commercial numerical simulator for a simple case. Then the transient pressure responses are calculated, and flowing patterns and characteristic flowing periods caused by MLHWs are analyzed. A parametric analysis is also conducted to screen the critical parameters affecting the performance of multilateral horizontal wells. Analysis results suggest that stress-sensitivity of reservoir permeability has significant influence on the performance of MLHWs in low-permeability reservoirs; the parameters related to the shape of MLHWs, such as branch length, branch spacing, the angles between branch and horizontal wellbore, also can obviously affect the transient pressure dynamics of MLHWs. The proposed model in this paper can accurately simulate the transient pressure behaviors of MLHWs. It can help better understand the flowing characteristics of MLHWs, provide more accurate dynamic parameters for reservoir development, and give some insight into the design of MLHWs to obtain higher recovery.

Solvent-Enhanced Steamdrive: Experiences From the First Field Pilot

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 175414, “Solvent-Enhanced Steamdrive: Experiences From the First Field Pilot in Canada,” by M.L. Verlaan, SPE, and R. Hedden, SPE, Shell Canada; and O. Castellanos Díaz, V. Lastovka, SPE, and C.A. Giraldo Sierra, Shell Chemicals Americas, prepared for the 2015 SPE Kuwait Oil and Gas Show, Mishref, Kuwait, 11–14 October. The paper has not been peer reviewed. In recent years, the addition of a hydrocarbon condensate to steam operations in heavy-oil and bitumen reservoirs has emerged as potential technology to improve not only oil recovery but also energy efficiency. The idea of solvent addition to a steamdrive process has been extended and applied for the first time in the Peace River area in Canada. There, evidence was obtained of oil uplift in the patterns where solvent was injected. However, piloting this new technology in a brownfield had many challenges, especially when evaluating its main economic factors: production increase and solvent recovery. Introduction Vertical-well steamdrive (VSD) is the selected process to recover bitumen from the Peace River Bluesky formation. Solvent coinjection has been identified as an economical method to improve the efficiency of this process. In an early phase of the steamdrive, a slug of hydrocarbon condensate (diluent) is coinjected with the steam. The solvent condenses at the cold steam/bitumen interface to form a solvent bank. This bank has the potential to accelerate bitumen production by viscosity reduction and to improve ultimate recovery. The efficiency of the diluent coinjection in a steamdrive process is expected to be lower than that of liquid addition to steam for enhanced recovery; however, the solvent recovery factors are expected to be much higher. The solvent recovery, therefore, is a key factor in the economic viability of the process. The main objectives of the pilot were to obtain a positive response in bitumen production and accurate quantification of the diluent recovery. An accurate assessment of the bitumen-production increase was not expected because of the small size of the pilot and lack of control patterns; hence, the injection slug size and concentration were designed to obtain a significant and measurable bitumen response. Pilot Design The Peace River lease in Alberta, Canada, has been subject to many well-and recovery-technology trials in the last 30 years. One of the technologies tried is cyclic steam stimulation (CSS) with multilateral horizontal wells. Pad 19 has been developed with so-called “soak radial wells”—four horizontal laterals in a cross pattern. Over a 9-year time frame, bitumen has been produced in seven to eight CSS cycles. With a recovery of less than 20% from the initial design, a part of the pad has been converted to a pattern steamdrive to increase recovery to more than 50%. Vertical injectors and producers are drilled to complete the 5-acre inverted- fivespot patterns. Vertical producers are perforated over almost the complete interval, while steam injectors have been completed with five limited-entry perforations (LEPs) to distribute the steam evenly over the entire reservoir interval.

Key technology for treating slack coal blockage in CBM recovery: A case study from multi-lateral horizontal wells in the Qinshui Basin

Due to the nature of coal bed, slack coal production is inevitable in gas recovery sby water drainage. When coalbed methane (CBM) wells are reentered after low energy exploitation and shut-in, the negative effect of slack coal production on productivity of CBM is irreversible. In this paper, the CBM occurrence characteristics and multi-lateral horizontal well trajectory in the Qinshui Basin, Shanxi Province, were analyzed. In the multi-lateral horizontal wells, the expected gas production rate could not be reached and the production rate after shut-in maintenance could not restore to the level before shut-in. The reason for these issues is that migration pathways in the reservoirs are blocked by slack coal deposits, while formation water and slack coal deposit accumulated at the troughs of horizontal sections enlarge the resistance for gas to flow into the bottom hole. Furthermore, three key technologies to deal with slack coal blockage were proposed. Firstly, CBM horizontal well trajectory should follow the principle of keeping the wellbores smooth and updip instead of being “wavy”, on the premise of guaranteeing CBM drilling rate. Secondly, the cavities of production wells, as an important part of multi-lateral horizontal wells, are capable of settling sand, and can be used for gas–liquid–solid separation. And thirdly, a tree-like horizontal well with its main hole set on stable seam top or floor, provides a stable well flushing passage for coal powder. This research provides a useful attempt in solving the problem of slack coal production in gas recovery by water drainage.

Transient pressure analysis of fishbone multi-lateral horizontal well with non-uniform flux density

Transient pressure analysis of fishbone multi-lateral horizontal well with non-uniform flux density

The fate of fracturing water: A field and simulation study

Hydraulic fracturing of multi-lateral horizontal wells for shale gas production usually requires a great amount of water. Field data indicate that only a small fraction of the injected water can be recovered during the clean-up phase. Especially, when shale oil and gas wells undergo month-long shut-in periods after multi-stage fracturing processes. Field data also indicate that in some wells, such shut-in episodes surprisingly increase the oil and gas flow rate. However, the fate of non-recovered water in the reservoir and the reasons behind increased early-time oil and gas production after a long shut-in period are poorly understood.In this paper, we first interpret the flowback data of a 18-well pad completed in the Horn River Basin. Then, we use a numerical simulator to investigate the parameters controlling water and gas production during the flowback process. In the simulation model, the shale reservoir is represented by a fracture–matrix model, where the fractures form a continuum of interconnected network. The simulation results show that the counter-current imbibition of fracturing water during the shut-in period can result in a significant gas build-up in the fractures and therefore increases early-time gas production rate. It was also concluded that early-time water and gas production depends on reservoir properties such as capillary pressure and complexity of created fracture network and operational parameters such as shut-in time. The gas production rates from reservoirs with higher capillary pressure is higher at the beginning of flowback process but the production rate falls later. The complexity of fracture network created during hydraulic fracturing process has a great effect on load recovery and gas production. As the complexity increases, the gas production rate increases and load recovery decreases due to higher contact surface created between fractures and shale matrices. Further, field data and simulation results show that extended shut-in period increases early-time gas production but it decreases load recovery and late-time gas production.

A numerical study of sequential and simultaneous hydraulic fracturing in single and multi-lateral horizontal wells

Abstract Horizontal well hydraulic fracturing (HF) technology can help to develop low permeability oil and gas resources. Today, industry uses simultaneous and sequential fracturing as a means to fracture single or multiple (Zipper Frac) horizontal wells as an efficient way to produce oil/gas. In zipper fracturing two or more parallel wells are fractured simultaneously or sequentially to achieve the maximum stimulated reservoir volume. In order to achieve optimum stimulated rock volumes and fracture networks, one must understand the effect of various rock and fluid properties on stimulation to minimize the risk of unwanted fracture geometries. This paper describes the development and application of a 2D coupled displacement discontinuity numerical model for simulating fracture propagation in simultaneous and sequential hydraulic fracture operations for single and multiple parallel wells. The sequential fracturing model considers two different boundary conditions for the previously created fractures. A constant pressure boundary condition along the fracture surface is considered when the flow back is restricted between the stages and a joint model is used when fractures are propped. A series of examples are presented to study the effect of fracture spacing on expected stimulated zone. It is found that fracture path is not only affected by fracture spacing but also by the boundary conditions on the previously created fractures.

A new attempt of a CBM tree-like horizontal well: A pilot case of Well ZS 1P-5H in the Qinshui Basin

A multi-lateral horizontal well is one of the main well types employed in the coal bed methane (CBM) development. In a traditional CBM multi-lateral horizontal well, either a major hole or laterals will go crossing through coal beds to the largest extent, which may eventually result in bed collapse, footage failing to meet the design requirement, and the major hole unable to be monitored, re-entered and flushed. Therefore, this paper puts forward a design idea of a tree-like horizontal well composed of a major hole (for dredging passage), laterals (for controlling drainage area) and sub-laterals (for enhancing production). The major hole is usually drilled on the stable roof or floor of a coal bed, laterals are drilled from the major hole into coal beds, and several sub-laterals are drilled from laterals. The major hole, laterals and sub-laterals constitute a tree-like drainage and recovery system, whose major hole remains stable for a long period and can be monitored and maintained. The technique has been successfully applied in Well ZS 1P-5H in the Qinshui Basin, Shanxi. The well included one major hole, 13 laterals, and 26 sub-laterals, with a total drilling footage of 12288 m, a total coal bed footage of 9512 m, and a total pure coal footage of 9408 m. Its major hole was fully placed in the mudstone of the coal bed roof. This well records a successful case of incident-free single well drilling with a footage of more than 10,000 m and serves as a new well type for efficient CBM development in China.

Productivity Prediction for Stacked Multilateral Horizontal Well Under Open Hole Series Completion Methods

Productivities of stacked multilateral horizontal well under open hole series completion methods were predicted by an analytical model. The analytical model was established using conformal transformation, mirror image, potential superposition and equivalent flow resistance. The ideal well’s formula will be simplified to the famous Borisove’s formula when stacked well has only one branch and locate it in middle vertical depth of reservoir. Several productivity influencing factors were analyzed to provide references for stacked well completion design. Case studies show that, stacked well productivity decreases with higher screen filtration precision; Conventional horizontal well productivity is more sensitive to filtration precision than that of stacked well; Stacked well’s vertical location in reservoir with upper and lower sealed boundary has little impact on productivity; Analytical model overestimates productivity because of ignorance of seepage disturbance and well bore flow pressure drop, an infinitesimal sectional model works as a correction model and a correction coefficient is obtained to effectively reduce the error of analytical model. Key words : Stacked well; Open hole; Analytical model; Mirror image; Potential superposition; Seepage resistance