Model For Horizontal Wells Research Articles

Analytical method for performance evaluation of fractured horizontal wells in tight reservoirs

This paper presents an analytical model for horizontal well with multiple hydraulic transverse fractures, producing from a tight oil reservoir. The model combines productivity index model (Guo et al.2009) with non-Darcy flow and fracture heterogeneity.Although there are numerous analytical models have been proposed for fractured horizontal wells performance, either pseudo-steady conditions or pressure-transient phenomenon. They rarely consider the influence of non-Darcy flow and fracture heterogeneity on fractured horizontal wells performance. Non-Darcy flow behavior has been proved to exist in tight reservoirs by many previous investigators. In the meantime, fracture heterogeneity should not be neglected in the process of hydraulic fracturing.In this paper, we deduce an analytical production equation in detail, towards fractured wells in tight reservoirs. Based on productivity index model, three flow region are analyzed by seepage characteristics. We make further analysis of pressure distribution in fractured horizontal well by a commercial numerical simulator. In addition, some critical factors on productivity have been considered.Results show that there are strong correlations between productivity and critical factors by the mathematical model. Further verification of the influences on well productivity is demonstrated. The fractured well productivity with different threshold pressure gradient and deformation coefficient has negative correlation. Fractured well productivity increases as fracture number, half of fracture length, and fracture conductivity increases within a certain range. The effect on fractured well productivity by fracture heterogeneity appears to be complex, not only by the end point influence, but also by fractures of internal interference.

Wellbore stability analysis for horizontal wells in shale formations

As a serious problem in drilling operation, wellbore instability restricts efficient development of shale gas, especially in formations with weak bedding planes which have strong strength anisotropies. The occurrence of bedding planes has significant influence on wellbore instability. Triaxial compressive tests have been carried out to study the effects of the orientation angle between the major principal stress direction and the weak bedding plane on the strengths of weak bedding shales. According to the laboratory test data, the strength of rock matrix and the strength of weak bedding planes were acquired, and failure criterion of rock matrix and weak bedding planes were established based on Mohr-Coulomb strength criteria. Based on the poroelasticity theory and rock strength theory, this paper proposed a wellbore instability analysis model for horizontal wells to reveal the combined effects of borehole trajectory, occurrence of stratification, strength of weak plane on wellbore instability. The results show that the shape of curve between peak compressive strength and orientation angle is ‘U-shaped’, and the bedding planes of weakness causing the strong strength anisotropies. When the bedding dip angle is greater than about 45°, the reasonable well azimuth angle would make wellbore stable. In addition, the directions of bedding planes and in-situ stresses pose the significant influences on wellbore instability. This paper provides a method for wellbore stability analysis of weak bedding formations which can help design mud density and well trajectory by elaborating all the effects of various parameters on wellbore stability.

Analytical coupled axial-radial semi-steady state productivity model for horizontal wells in anisotropic medium

The classical productivity models are solutions to one-dimensional radial flow equations for vertical wells at different flow conditions. A new, fully analytical model for coupled radial well inflow and axial reservoir flow has been developed under the assumption of semi-steady state flow, i.e. the axial flow and the well inflow are solved simultaneously in closed form expressions. This coupled axial-radial flow model results in a quadratic pressure profile in the axial direction and a quadratic-logarithmic pressure profile in the radial direction. The new productivity equations are formulated by using either external pressure or average reservoir pressure in addition to flowing wellbore pressure. For the special case where axial flow or radial flow is zero, it is shown that the formulas coincide with the classical formulas for radial and linear flow, respectively. The new productivity model is also developed for an anisotropic medium by implementing a space transformation in the near-well region. The anisotropic productivity model highlights the flow in the near-well region and provides flexibility in choosing configuration of near-well simulation grid blocks. An algorithm for the simulation of the near-well flow and horizontal well productivity is presented.

Analytical coupled axial-radial semi-steady state productivity model for horizontal wells in anisotropic medium

Analytical coupled axial-radial semi-steady state productivity model for horizontal wells in anisotropic medium

Productivity model of horizontal wells in a sour gas reservoir

ABSTRACTThe utilization of a horizontal well has a great significance in the development of sour gas reservoir. The accurate prediction of the productivity of horizontal well will become more and more important in developing sour gas reservoir. In this paper, the effect of sulfur deposition on permeability is considered and a productivity prediction formula of the horizontal well is established. The effects of the length of horizontal well, the effective thickness of the reservoir, elemental sulfur deposition, and reservoir heterogeneity on productivity are analyzed and calculated. The theoretical results show that elemental sulfur disposition and the heterogeneity are the most important factors. According to the field case, the calculating results of improved Joshi’s equation approaches the real productivity, which means that it could be used to predict the productivity of horizontal well at initial stage during sour gas reservoir development. The results can be used as a reference for the development of similar sour gas reservoir.

A Coupled Reservoir/Wellbore Model to Simulate the Steam Injection Performance of Horizontal Wells

AbstractA coupled reservoir/wellbore model of horizontal wells in a steam injection process is presented, which considers the three‐dimensional simultaneous flow of three phases in the reservoir and gas–liquid two‐phase flow in the wellbore. Based on the model, the steam injection performance of a horizontal well is simulated. The pressure, temperature, and steam quality distribution in the wellbore as well as the steam injection profile and reservoir temperature along the horizontal wellbore are discussed. Results show that the wellbore pressure, temperature, and steam quality decrease from the horizontal wellbore heel to the toe. The steam flux rate and reservoir temperature are higher at the wellbore heel and toe. Furthermore, the variations of the steam flux rate and reservoir temperature along the wellbore increase with sustained injections, which is a disadvantage for thermal horizontal wells. Therefore, developing techniques to guarantee a uniform flow along horizontal wellbores is crucial.

A collapse pressure prediction model for horizontal shale gas wells with multiple weak planes

Since collapse of horizontal wellbore through long brittle shale interval is a major problem, the occurrence characteristics of weak planes were analyzed according to outcrop, core, and SEM and FMI data of shale rocks. A strength analysis method was developed for shale rocks with multiple weak planes based on weak-plane strength theory. An analysis was also conducted of the strength characteristics of shale rocks with uniform distribution of multiple weak planes. A collapse pressure prediction model for horizontal wells in shale formation with multiple weak planes was established, which takes into consideration the occurrence of each weak plane, wellbore stress condition, borehole azimuth, and in-situ stress azimuth. Finally, a case study of a horizontal shale gas well in southern Sichuan Basin was conducted. The results show that the intersection angle between the shale bedding plane and the structural fracture is generally large (nearly orthogonal); with the increase of weak plane number, the strength of rock mass declines sharply and is more heavily influenced by weak planes; when there are more than four weak planes, the rock strength tends to be isotropic and the whole strength of rock mass is greatly weakened, significantly increasing the risk of wellbore collapse. With the increase of weak plane number, the drilling fluid density (collapse pressure) to keep borehole stability goes up gradually. For instance, the collapse pressure is 1.04 g/cm3 when there are no weak planes, and 1.55 g/cm3 when there is one weak plane, and 1.84 g/cm3 when there are two weak planes. The collapse pressure prediction model for horizontal wells proposed in this paper presented results in better agreement with those in actual situation. This model, more accurate and practical than traditional models, can effectively improve the accuracy of wellbore collapse pressure prediction of horizontal shale gas wells.

A coupling model for horizontal well in heterogeneous box-shaped reservoir

A coupling model for horizontal well in heterogeneous box-shaped reservoir

A Semianalytical Model for Horizontal Wells With Improved Stinger Completion in Heterogeneous Bottomwater Reservoirs

Summary Stinger-completion technology is simple to operate and low cost, which can achieve good results in stable oil production by controlling water cut in a bottomwater reservoir. However, most previous studies of stinger completions took place in homogeneous reservoirs and are not equipped to deal with the multipoint watercresting breakthrough caused by fractures or permeability contrast in a heterogeneous bottomwater reservoir. A new improvedstinger- completion (ISC) semianalytical coupled model of reservoir and wellbore flow is established in this article, which considers the impacts of well trajectory, permeability distribution, formation damage caused by drilling and completion, and variable mass flow in a horizontal wellbore. By discrete numerical calculation of the new model, pressure, inflow, and water-cresting profiles can be acquired, and consequently, a design method of ISC is also proposed to be used successfully in a heterogeneous bottomwater reservoir for stable oil production by water-cut control and by optimizing the structure, length, and diameter of the stinger. The successful field application of ISC in the LU-X horizontal well also confirms the feasibility and effectiveness of ISC.

Water Breakthrough Shape Description of Horizontal Wells in Bottom-Water Reservoir

Horizontal wells have been applied in bottom-water reservoir since their advantages were found on distribution of linear dropdown near wellbore, higher critical production, and more OOIP (original oil in place) controlled. In the paper, one 3D visible physical model of horizontal physical model is designed and built to simulate the water cresting process during the horizontal well producing and find water breakthrough point in homogenous and heterogeneous reservoir with bottom water. Water cresting shape and water cut of horizontal well in between homogenous and heterogeneous reservoir are compared on the base of experiment’s result. The water cresting pattern of horizontal well in homogeneous reservoir can be summarized as “central breakthrough, lateral expansion, thorough flooding, and then flank uplifting.” Furthermore, a simple analysis model of horizontal well in bottom water reservoir is established and water breakthrough point is analyzed. It can be drawn from the analysis result that whether or not to consider the top and bottom border, breakthrough would be located in the middle of horizontal segment with equal flow velocity distribution.

Fracture Parameters Optimization of BZ Oilfield Horizontal Well Integral Fracturing

Horizontal well technology has become an important technological means for offshore oilfield exploitation, but at present, most of the fracture parameters optimization of horizontal well fracturing are based on the single wells productivity after fracturing and pay less attention to consider the impact of injection wells.Therefore, aiming at injection and production development mode of BZ oilfield horizontal wells after fracturing, Integral fracturing physical model and productivity forecast mathematical model of horizontal well for the purpose of improving integrated exploitation benefit of the block is established respectively.Combining with reservoir parameters of BZ oilfield, a corresponding numerical simulator is developed by means of solving mathematical model to forecast production performance of oil well with different fracture number, fracture length, fracture conductivity. The best fracture parameters are obtained through analyzing the effect of fracture parameters on accumulative oil production, which provides theoretical foundation for integral fracturing optimization design of horizontal well of BZ oilfields, and has vital site guiding significance.

Water shut off in a horizontal well: Lab experiments with starch graft copolymer agent

Abstract A kind of starch graft copolymer (SGC) water shut off agent, a novel, efficient and economic crude macromolecular plugging agent, has been applied to some oilfields. In this paper, a three dimensional physical model of horizontal well was designed for the water shutoff with an edge water simulating the edge water driving reservoir and with a higher permeability band imitating the preferential paths. Using the model and X-ray computed tomography (CT), the effect of blocking the water channeling paths on the model taken by starch strong gels blocking agent was tested. The result showed that the agent was selective and got a good effect. Besides, a simple Computer Modeling Group (CMG) model was used to deduce the development process of the water breakthrough, channeling, and flooding, so as to explain previously what had happened in the physical model. Finally, compared to field experiment, the advance of the model lies in that it can be used in performance appreciation of water shut off agent well.

Productivity prediction model and optimal configuration of herringbone multilateral well

In order to accurately predict the productivity of herringbone multilateral well, a new productivity prediction model was founded. And based on this model, orthogonal test and multiple factor variance analysis were applied to study optimization design of herringbone multilateral well. According to the characteristics of herringbone multilateral well, by using pressure superposition and mirror image reflection theory, the coupled model of herringbone multilateral well was developed on the basis of a three-dimensional pseudo-pressure distribution model for horizontal wells. The model was formulated in consideration of friction loss, acceleration loss of the wellbore and mixed loss at the confluence of main wellbore and branched one. After mathematical simulation on productivity of the herringbone multilateral well with the coupled model, the effects of well configuration on productivity were analyzed. The results show that lateral number is the most important factor, length of main wellbore and length of branched wellbore are the secondary ones, angle between main and branched one has the least influence.

Sectional Optimization Study on Perforation Parameters of Horizontal Wells in DaQing Oilfield

A coupled model for horizontal wells with perforation completion was built by combing the flow models in reservoir and wellbore. Then used the genetic algorithm to determine the flow rate and pressure distribution along the wellbore. The influence of the length and position of the perforation section to the production ability was also studied. The partition perforation optimization technique can uniform the inflow profile along the horizontal wellbore, prolong the develop cycle, and increase the development benefit.

Segmentally variable density perforation optimization model for horizontal wells in heterogeneous reservoirs

Abstract A 3D three-phase segmentally variable density perforation optimization model for horizontal wells is built by coupling reservoir fluid filtration, near wellbore inflow and wellbore conduit flow based on reservoir numerical simulation. The effects of 8 factors (filtration difference between heel/toe and middle intervals, imperforated interval, permeability heterogeneity, oil layer thickness heterogeneity, porosity heterogeneity, wellbore pressure drawdown, maximum perforation density, and perforation optimization principles) on perforation density and inflow profile, and that of fluid viscosity, casing diameter and pipe wall coarseness on well bore pressure drawdown, are analyzed for segmentally variable density perforation of horizontal wells. Results show that filtration difference between heel/toe and middle intervals, imperforated interval, permeability heterogeneity and oil layer thickness heterogeneity have significant effects on segmentally variable density perforation. In particular, different perforation density optimizations may occur when filtration difference between heel/toe and middle interval is not considered; imperforated interval may affect inflow profile; well bore pressure drawdown can be ruled out for segmentally variable density perforation of most horizontal wells onshore in China. The contrast between predicted and actual production of Well AT9-7H in the Tahe Oilfield indicates that the model is highly accurate.

Comparative Study on Inflow Performance Model of Short Horizontal Wells

High yields and higher efficiency can be acquired by using horizontal well as it has a lager contact area reservoir. So the horizontal well has become a better choice to gas fields all over the world, especially to low permeability oil fields in the world. There are several inflow performance models for horizontal wells. This paper studies several horizontal well models currently widely used in the word through an example of Chinese oil field. These include steady state model of Giger model, Joshi model and Renard and Dupuy model. And pseudo steady model of Babu and Odeh model. The results show that Giger model give greater production rate from our procedure and calculation.

Integration of Production Analysis and Rate/Time Analysis by Use of Parametric Correlations - Theoretical Considerations and Practical Applications

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 140556, ’Integration of Production Analysis and Rate/ Time Analysis by Use of Parametric Correlations - Theoretical Considerations and Practical Applications,’ by D. Ilk, SPE, Texas A&M University/DeGolyer and MacNaughton; J.A. Rushing, SPE, Apache Corporation; and T.A. Blasingame, SPE, Texas A&M University, prepared for the 2011 SPE Hydraulic Fracturing Technology Conference and Exhibition, The Woodlands, Texas, 24-26 January. The paper has not been peer reviewed. Well-performance analysis in unconventional reservoirs is a challenging task because of the nonuniqueness associated with estimating well and formation properties. Also, estimating of reserves can be uncertain because of the very long transient-flow periods. Recent semiempirical rate/time relations have been shown to model the rate/time behavior properly for wells in unconventional reservoirs. This study focused on finding theoretical and empirical relationships of rate/time-model parameters with well and formation properties. Introduction Unconventional-reservoir systems (e.g., tight-gas-sand, shale-gas, tight/shale-oil, and coalbed-methane reservoirs) have become a significant source of hydrocarbon production, and they offer high potential for reserves growth and future production. Complex geological and petrophysical systems describe unconventional reservoirs in addition to heterogeneities at all scales similar to conventional-reservoir systems. Because of the low-to-ultralow permeability, well-stimulation operations (e.g., single or multistage hydraulic fracturing) are required to establish production at commercial rates. Analytical and semianalytical modeling of horizontal wells connected to multiple transverse fractures is important in terms of diagnosing well-performance behavior. At early time, the dominant flow is linear (perpendicular to the fracture face) until pressure transients of the individual fractures begin to interfere, leading to a compound-linear-flow regime. A semianalytical solution can model the entire range of flow regimes surrounding a horizontal well with multiple fractures. The solution includes a dual-permeability region near fracture faces to represent the complex fractured region surrounding the primary planar hydraulic fractures. Reserves estimation for unconventional-reservoir systems has been performed primarily by use of conventional Arps’ decline-curve relations. Application of Arps’ relations (specifically the hyperbolic relation) for reserves estimates yields significant overestimates of reserves because Arps’ relations are applicable only during a boundary-dominated-flow regime, whereas unconventional-reservoir systems exhibit extremely long transient-flow periods. Recently, two rate/time relations were introduced to estimate reserves in unconventional reservoirs in the form of the “stretched exponential function.” These relations have proved to be successful in modeling the rate/time behavior properly, and these relations provide consistent and more-realistic reserves estimates compared with Arps’ decline relations.

Generalized inflow performance relationships for horizontal gas wells

The analytical inflow performance relationships (IPRs) of horizontal gas wells are presented in this paper for different reservoir boundary conditions. Even though reservoir simulation models (numerical models) may give more flexibility and detailed results of oil and gas production, analytical models are commonly used in the field for quick, practical and reasonable estimation of well performance. The analytical models are especially attractive when working on single well design and performance optimization. Similar to vertical well models, the analytical models for horizontal wells are developed for specific conditions. The IPR equations for horizontal gas wells are categorized into three boundary conditions; constant boundary pressure (steady-state flow condition), no-flow boundary (pseudo-steady-state flow condition), infinite acting reservoir (transient flow condition). For each condition, the IPR equations of horizontal gas wells are presented and the limitation and appropriate application are discussed carefully. Moreover, this paper discusses the effect of critical parameters such as permeability anisotropy, wellbore length, non-Darcy flow and near wellbore formation damage on the inflow performance of horizontal gas wells. These equations provide the reservoir and production engineers with an invaluable tool in well structure design, development plan, and their daily practice dealing with horizontal wells.

Developing a Tool for 3D Reservoir Simulation of Hydraulically Fractured Wells

Summary This paper describes the development and capabilities of a novel and unique tool that interfaces a hydraulic fracture model and a reservoir simulator. This new tool is another step in improving both the efficiency and consistency of connecting hydraulic fracture engineering and reservoir engineering. The typical way to model hydraulically fractured wells in 3D reservoir simulators is to approximate the fracture behavior with a modified skin or productivity index (PI). Neither method captures all the important physics of flow into and through the fracture. This becomes even more critical in cases of multiphase flow and multilayered reservoirs. Modeling the cleanup phase following hydraulic fracture treatments can be very important in tight gas reservoirs, and this also requires a more detailed simulation of the fracture. Realistic modeling of horizontal wells with multiple hydraulic fractures is another capability that is needed in the industry. This capability requires more than an approximate description of the fracture(s) in the reservoir-simulation model. To achieve all the capabilities mentioned above, a new tool was developed within a commercial lumped 3D fracture-simulation model. This new tool enables significantly more accurate prediction of post-fracture performance with a commercial reservoir simulator. The automatically generated reservoir simulator input files represent the geometry and hydraulic properties of the reservoir, the fracture, the damaged zone around the fracture, and the initial pressure and filtrate fluid distribution in the reservoir. Consistency with the fracture-simulation inputs and outputs is assured because the software automatically transfers the information. High-permeability gridblocks that capture the 2D variation of the fracture conductivity within the reservoir simulator input files represent the fracture. If the fracture width used in the reservoir model is larger than the actual fracture width, the permeability and porosity of the fracture blocks are reduced to maintain the transmissibility and porous volume of the actual fracture. Both proppant and acid fracturing are handled with this approach. To capture the changes in fracture conductivity over time as the bottomhole flowing pressure (BHFP) changes, the pressure-dependent behavior of the fracture is passed to the reservoir simulator. Local grid refinement (LGR) is used in the region of the wellbore and the fracture tip, as well as in the blocks adjacent to the fracture plane. Using small gridblocks adjacent to the fracture plane is needed for an adequate representation of the filtrate-invaded zone using the leakoff depth distribution provided by the fracture simulator. The reservoir simulator input can be created for multiphase fluid systems with multiple layers and different permeabilities. In addition, different capillary pressure and relative permeability saturation functions for each layer are allowed.

Horizontal well pressure analysis in box-bounded reservoirs

In this paper, solutions to the 3D transient flow mathematical model for horizontal wells in box-rounded reservoirs are presented. The solutions are derived in Laplace transform domain by employing integral transform and point-source superposition. Both efficient computation of pressure responses and practical technology of oil field application mentioned here may be used to interpret the data from unsteady-state horizontal well testing.