This paper takes a novel approach towards managing the architecture and protocol of injection/production system. The shut-in valve positioning and time of valve closure control the amplitude and frequency of pressure waves generated during shutdowns. The proposed approach provides the means for mitigating negative impact of water hammer on the integrity of near wellbore region and the intensity of cross-flow. It is based on a comprehensive model of fast wellbore transients (water hammer) generated by routine or emergency shutdown of injector or producer and interacting with a near wellbore reservoir region. The modeling handles the conventional transient pipe flow hydraulics coupled with the transient reservoir flow. The decompression wave created by shutting down an injector interacts with the near wellbore region and may induce a transient flow back from reservoir creating a risk of mechanical damage and sand production. The compression wave created by shutting down a producer may induce repeated injection pulses. In both cases, multiple cross-flow phenomena can be triggered between formation layers and wells interconnected within the injection or production system. The analysis of these transient phenomena helps to potentially quantify the mechanical damage, which may be induced in near wellbore reservoir region, and assess the potential damage risk associated with produced solids.
Zhang, Ke (Rice University) | Chanpura, Rajesh A. (Schlumberger) | Mondal, Somnath (University of Texas at Austin) | Wu, Chu-Hsiang (University of Texas at Austin) | Sharma, Mukul M. (University of Texas at Austin) | Ayoub, Joseph A. (Schlumberger) | Parlar, Mehmet (Schlumberger)
Particle size distribution (PSD) is used for various purposes in sand control: decision between various sand control techniques (e.g., Tiffin criteria), sizing of the filter media (sand screens and/or gravel packs) through either rules of thumb (Coberly, 1937; Saucier, 1974; etc.) or physical experiments or theoretical models (Chanpura et al., 2012, 2013; Somnath et al., 2011, 2012). PSD of formation sand samples are also often used to generate “simulated” formation sand for laboratory experiments. Two most commonly used techniques for PSD measurements are sieve and laser, while some engineers use one technique for no obvious or justifiable reasons, others use both techniques for measurements and don’t know what to do with the data when significant differences exist in PSDs obtained from each technique. Although the inherent limitations of, and the differences between, these two techniques as well as other factors impacting the measurements are well known, a systematic study as to what is relevant to sand control along with when and why is lacking. In this paper, we critically review the current practices in PSD determination and use and misuse of the information obtained from those measurements, propose a methodology towards determination of what is relevant, when and why, and present our initial experimental results that support our conclusions.
Restrepo, Alejandro (Equion Energia ) | Ocampo, Alonso (Equion Energia) | Lopera, Sergio (Universidad Nacional De Colombia) | Coronado, Jorge L. (Equion Energia ) | Sanabria, Rosa B. (Equion Energia) | Alzate, Luis G. (Equion Energia ) | Hernandez, Sergio (Equion Energia)
The following paper is the continuation of SPE Paper 152309 (GaStim Concept - A Novel Technique for Well Stimulation. Part I: Understanding the Physics) and contains the experimental work and field pilot testing stages of the GaStimulation method already proposed by the authors. Systems studied correspond to tight quartzarenites containing retrograde gas condensates exhibiting Krg impairment under depletion. In this type of systems treatment penetration and durability are key factors for benefit sustainment. Supported by the theoretical background and preliminary lab tests presented in part I (SPE152309), the second stage of the GaStim project was planned and executed covering the phases of product´s screening, well candidate selection, pilots´ execution and results evaluation. Two pilots are reported, one in which water induced blockage is removed by stand-alone gas injection and another in which deep Gas + chemical dispersion is injected to reach a condensate blockage damage radius of 100 ft +. In the first scenario, it is noted that Sw reduction / Kg improvement is attained in the gastimulated area probably by coupled effects of evaporation and water slug displacement. In condensate blockage scenarios, it was noted that micellar type of surfactants exhibit the best performance when tested against IFT reduction capacity, Kg re-establishment (after condensate and water blockage) and treatment durability. Additionally, it was observed that the tuning of chemical concentrations and deployment method is key to maximize hydrocarbon flow capacity and minimize emulsion effects at surface after gastimulation. Further experimental work is planned to support modelling approaches both aimed on improving design criteria and expanding the potential of the technique into more challenging environments.
Calcada, L. A. (Federal Rural University of Rio de Janeiro) | Scheid, C. M. (Federal Rural University of Rio de Janeiro) | Calabrez, N. D. (Federal Rural University of Rio de Janeiro) | Waldmann, A.T.A. (Petrobras ) | Martins, A. L. (Petrobras )
Fluid filtration and invasion occur in drilling oil wells operations in overbalanced conditions. In static and dynamic condition, the buildup of a porous and compressible cake on the wall of the well avoids the inadequate invasion and possible damage to the reservoir. The composition of the drilling fluid and operational conditions affect the mud cake build up and its properties as permeability, porosity and compressibility. Consequently, these parameters are important in the determination of the filtrate and fluid invasion. The main objective of this work was to evaluate the filtrate parameters and propose a simplified model and methodology to simulate that process. In this study, both real drilling fluids and fluids prepared in laboratory were considered. The experiments for parameter evaluation were conducted in a filtration cell HTHP (high temperature / high pressure) using filter paper as filter medium.
The simplified methodology and model presented hereby are useful in the estimation of the amount of filtrate and the invasion of the drilling fluids in the process of drilling of oil wells.
The mathematical model for filtration and fluid invasion calculation was based in mass and momentum conservation equations and hydraulic equations. Based on the experimental data and mathematical model, mud cake parameters were determined, such as permeability, porosity, compressibility, thickness and friction factor. The simulations results showed a good agreement between field and simulated data.
Combining the proposed simplified model/methodology and the mud cake and the reservoir rocks properties, it was possible to simulate and to estimate the filtration and fluid invasion in different conditions that allows optimum design of bridging agents for drill-in fluids.
Stimulation results of carbonate matrix acidizing are strongly dependent on the acid injection rate. Numerous studies have shown that an optimum interstitial velocity (Vi-opt, injection rate over flow area and porosity) exists, which results in the minimum volume of acid required for wormhole propagation and best stimulation results. During the last decade, much progress has been made to determine the factors that affect the optimal conditions in linear coreflood experiments, including the temperature, acid type, and acid concentration. However, little work has focused on the effects of the core dimensions, although a core-size dependence has already been observed. It has been shown that for a fixed core diameter, the Vi-opt
increases with increasing core length, but it is not clear if the Vi-opt can be independent of the core length when the core length reaches a certain value. In this work, we conducted a series of coreflood experiments with Indiana limestone cores at room temperature. The cores are selected homogeneous ones, thus to eliminate the effect of heterogeneity. The acid was 15% plain hydrochloric acid. The core lengths range from 4-in. to 10-in. and the core diameters were 1-in., 1.5-in. and 4-in.
For the 1-in. and 1.5-in. diameter cores, we found that the optimal conditions changed as core length increased for lengths less than 6 inches. The optimal flux was found to scale with core diameter, as found in other recent studies. In the paper, we show how these results improve scale-up of laboratory acidizing results to the field scale.
With gas production from gas condensate reservoirs, the flowing bottomhole pressure of the production well decreases. When the flowing bottomhole pressure becomes less than the dew point pressure, condensate accumulates near the wellbore area and forms a condensate bank. This results in loss of productivity of both gas and condensate. This becomes more serious in intermediate permeability gas-condensate reservoirs where the condensate bank reduces both the gas permeability and the well productivity.
Several techniques have been used to mitigate this problem. These methods include: gas cycling, drilling horizontal wells, hydraulic fracturing, injection of super critical CO2, use of solvents and the use of wettability alteration chemicals. Gas cycling aims to keep the pressure of the reservoir above the dew point pressure to reduce the condensation phenomena. The limited volumes of gas that can be recycled in the reservoir can hinder the application of this method. In order for an ideal recycle, gas volume injected into the reservoir will be larger than the total gas that can be produced from such a reservoir. Other approaches are drilling horizontal wells and hydraulic fracturing where the pressure drop around the wellbore area is lowered to allow for a longer production time with only single phase gas flow to the wellbore. These approaches are costly as they require drilling rigs. Another technique is the use of solvents which shows good treatment outcomes, but the durability is a questionable issue in these treatments. Moreover, wettability alteration needs to be approached very carefully as to not cause permanent damages to the reservoir. It was reported in many studies the use of fluorinated polymers and surfactants dissolved in alcohol-based solvents for wettability alterations treatments.
Each method has its own advantages and disadvantages, and can be applied under certain conditions. The paper presents all of these methods along with their advantages and disadvantages, besides description of some of their field applications and case studies.
Mesophase technology for wellbore clean-up and remediation in the drilling industry has been used in various oil fields to increase well productivity and injectivity. The majority of these applications include oil-based mud filter cake removal, near-wellbore remediation, and wellbore displacement.
The open hole wells completed with standalone screens in the deepwater tertiary formations offshore West Africa have benefited from previous knowledge and experiences accumulated by the operator and the service company in the application of Mesophase technology in other fields.
This paper discusses the field application of the Mesophase technology in several deepwater offshore fields in West Africa. Previous to the field application, the Mesophase formulation was customized for the field conditions, such as temperature, fluid density, type of completion brine, and specific oil-based mud. The customized formulation was evaluated to determine the regain of injection permeability, fluid compatibility and the breakthrough time. Intensive tests were required to fine-tune the formulation to obtain the desired high-injection permeability for the challenging conditions encountered in the field.
Results from the laboratory and description of the field application are discussed and presented in this paper. The field applications data proved that, after placement of the mesophase treatment in the wells, diffusion of the treatment produced: (1) break-up of blocking solids from the completion screens; (2) removal of filter cake residues; and (3) water-wetting of all solid surfaces. This cleaning treatment gave very good results in the production and water-injection wells.
Further advancement of prediction methods for wellbore stability requires a detailed description of fluid motion in the invasion zone and the development of real-time algorithms. Such algorithms should be based on a reliable model of motion and interaction of the fluids and pore space. This joint general deformation model should be approximated to obtain a number of reduced models that one can use for less-accurate but quick calculation of the near wellbore parameters. The objective of our research is to study the stress-deformed state of a porous medium saturated with fluids with the basic assumption that there is a number of different spatial scales porous medium deformation and fluid filtration flow. The general model is based on the principles of continuum mechanics and deformation of interpenetration continuums. A small parameter expansion method is applied for a dimensionless equation system. This method will use a relation of the spatial scales of deformation of the solid components and fluid flow.
The coupled models of fluid filtration in deformed media can be widely applied in the oil and gas industry, mining, medicine and hydrogeology. The approximated models can be used in software products for fast estimation of wellbore stability.
An initial sequence of models has been determined, corresponding to different approximations for the small parameter, where the zero-approximation model describes constant-volume deformation of a porous material. In this case the porous-pressure equation is separated from the matrix-deformation model. For the zero-approximation a number of analytical solutions were obtained in particular, in cylindrical coordinates, to describe the stress-deformed state around a vertical well. These solutions contain the non-zero shear stresses able to cause the formation damage. The first-approximation equations for incompressible saturating phases have transferred into a system similar to the Buckley-Leverett equations of two-phase filtration, but written for a deformed porous medium.
The zero-approximation poroelastic solutions are valuable as a class of non-one-dimensional approximations of motions of a porous material in a medium with constant volume. The zero- and first-approximation equations are enough to develop the fast numerical algorithm, for they can be used to estimate the areas of possible matrix destruction.
Gupta, Shilpi (Schlumberger ) | Sinha, Ravi (Schlumberger) | Verma, Vibhor (Schlumberger) | Kumar, Ajit (Schlumberger ) | Singh, R.K. (Schlumberger) | Swain, Saraswat (Schlumberger) | Pandey, Arun (Schlumberger) | Majithia, P.P. Singh (Oil and Natural Gas Corporation) | Hinge, P. (Oil and Natural Gas Corporation)
Field XYZ located in the western offshore India is a multi-pay, multi-layered heterogeneous Carbonate reservoir having lateral discontinuities. Discontinuous layers and scale deposition and near well bore damage have led to multi-dimensional problems related to both upper and lower completions reducing ultimate field recovery. Workover attempts like re-perforation, additional perforations and plugging, artificial lift by electrical submersible pump (ESP) and secondary recovery by water injection were implemented to maximize the field recovery. However, any work over had only short term impact on production increase and water injection and ESP performance were inefficient. Production History showed cyclic decline in production with time. Identifying and locating the layers’ discontinuities became crucial in candidate selection and design of efficient injection pattern, artificial lift, completion and work over in existing and new infill wells.
The following case study presents a workflow involving multi well geological, petro physical and time lapse formation pressure data and production logs to identify and locate lateral discontinuity within a pay of the field. The reservoir pressure support attempts using water injection methods were proved to be inefficient. Furthermore, this workflow has been successfully implemented for candidate well selection and designs the artificial lift using ESP.
An effective ESP design for three wells was implemented and seven future candidates for ESP were recognized. Additionally, locations of three new infill wells are identified and a strategic layer wise completion was designed.
Implementation of the results increased production from the field by 30%.
Ling, Kegang (University of North Dakota) | Zhang, He (Weatherford) | Shen, Zheng (Weatherford) | Ghalambor, Ali (Oil Center Research International) | Han, Guoqing (China University of Petroleum Beijing) | He, Jun (University of North Dakota) | Pei, Peng (University of North Dakota)
Formation damage caused by overbalanced drilling (OBD) using water-based mud (WBM) is inevitable as a result of mud filtrate invading into the near wellbore formation. The invasion radius is critical to the multiphase flow when the well is put on production. It contributes to the total skin that hinders the hydrocarbon production. Furthermore, the response of the logging tools may be affected as a result of such invasion, rendering many inaccurate calculations of the formation evaluation. To evaluate the skin caused by mud filtrate invasion, it is imperative to determine the radius of invasion properly. A thoroughly literature review indicated that the previous investigations have focused on formation damage caused by drilling mud filtration, and none of them had proposed a practical, comprehensive, and reliable method, with solid theoretical base, to quantify this formation damage. This work filled this gap.
In this work, we developed a practical and comprehensive model to determine the depth of mud filtrate invasion near the wellbore. The distribution of mud filtrate saturation in the near-wellbore region is also calculated by employing drilling operation parameters, mud filtration test data, relative permeability, and drilling time. With the accurately determined invasion radius, skin factor can be evaluated confidently. Then the well stimulation can be planned accordingly and appropriately, if it is necessary to remove or alleviate formation damage. Therefore, this work is significant in skin calculation and well stimulation design. It can also be used to estimate the cleanup period at the beginning of production, and allows engineers to predict the well performance and diagnose wellbore problems by checking any deviation from the predicted production. This study can also assist with the correction of parameters inferred from log measurements, thereby reducing the over and/or underestimation of log derived parameters used in various formation evaluation calculations.