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Ribeiro, Ayrton (The University of Queensland Centre for Natural Gas Energi Simulation Research Fellow, The University of Queensland) | Santiago, Vanessa (School of Chemical Engineering, The University of Queensland) | You, Zhenjiang (School of Chemical Engineering, The University of Queensland) | Johnson Jr, Raymond (School of Chemical Engineering, The University of Queensland The University of Queensland Centre for Natural Gas) | Hurter, Suzanne (The University of Queensland Centre for Natural Gas)
Stress-dependent permeability in coal seam gas (CSG) reservoirs can challenge the development of coal fields with lower initial permeabilities. Thus, advanced well stimulation techniques become essential. This work evaluates the performance of novel graded proppant injection (GPI) technique for CSG reservoir stimulation using reservoir simulation models. A simplified model for steady-state incompressible fluid flow during the early dewatering stage of production is validated by the analytical model results. A general model is then developed for GPI process during unsteady-state compressible two-phase flow in coal, accounting for gas desorption, matrix shrinkage, heterogeneous permeability distribution, and cross-flow. Fractured porous medium is modelled by a dual-porosity radial model. Stress-dependent permeability and matrix shrinkage effects are modelled using the Palmer-Mansoori equation. Under the incompressible fluid flow condition, the productivity index after well stimulation using GPI technique increases by 1.3~2.3 times. Moreover, simulation of compressible gas-water flow coupled with gas desorption from matrix yields 4~13% increment on recovery factor (RF) during production for 30 years. Stimulation accounting for matrix shrinkage enhances RF by 9~13%. For heterogeneous permeability distribution, more permeable layers exhibit deeper penetration of particles. The enhanced permeability owing to GPI yields higher production of both gas and water. Cross-flow between the coal layers influence the effectiveness of the depressurisation process and hence gas desorption post-stimulation. It allows dewatering of deeper layers and additional desorption of gas.
Produced water chemical compositional data are collected from a carbonate reservoir which had been flooded by North Seawater for more than 20 years, so there is an opportunity to analyse the large amount of produced water data collected, understand the brine/brine and brine/rock interactions and explore the impact factors behind them. In some publications, core flood experimental tests were performed with chalk cores or carbonate columns in order to make an understanding of possible chemical reactions occurring triggered by injected water with different composition (Seawater, low salinity water or any other brine). However, most of the time the laboratory conditions where core flooding experiments are implemented cannot fully simulate the real reservoir conditions. Therefore, in this study, with the help of the valuable produced water dataset and some basic reservoir properties, a one-dimensional reactive transport model is developed to identify what in situ reactions were taking place in the carbonate reservoir triggered by seawater injection. From the perspective of reservoir mineralogy, calcite, as the dominant mineral in the carbonate reservoir, is relatively more chemically reactive than quartz and feldspar which are usually found in sandstone. Whether calcite is initially and dominantly present in the carbonate reservoir rock is dissolved under seawater flooding or not is the first key issue we focused on. The effects of calcite dissolution on the sulphate scaling reactions due to incompatible brine mixing and the potential occurrence of carbonate mineral precipitation induced by calcite dissolution are investigated and discussed in detail.
Hydraulic fracturing for shale gas production involves pumping large volumes of water; as a consequence of this, produced water management is an important topic to address in order to sustainably produce shale gas. It has been well documented that only approximately 10-40% of the pumped fluids will be produced back to the surface, and that there will be increased concentrations of various ions in the flowback water during this process. This flowback water, with high total dissolved solids and high concentrations of certain ions, presents a significant risk of mineral scaling (
In general, it can be very challenging to identify the
A further two-phase 3D flow model was developed to examine the scaling tendency due to the evolving produced brine composition over the lifetime of the well. It is based on the previously history matched model and includes the fracture fluid and formation water compositions to predict precipitation of minerals. Finally, scale inhibitor injection was simulated to examine the impact of inhibitor retention on well protection.
The evidence from the produced-brine chemistry suggests that the Gyda field has experienced a variety of geochemical reactions caused by the high temperature and initial calcium (Ca) concentration, and so it is worth reviewing the produced-water data set and studying what in-situ geochemical reactions may be taking place.
Produced-brine-chemistry data from 16 wells in the Gyda field are plotted and analyzed in combination with general geological information and the reservoir description. A 1D reactive-transport model is developed to identify the possible geochemical reactions occurring within the reservoir triggered by seawater injection, and then extended with the inclusion of thermal modeling and also to be a 2D vertical-cross-section model.
Three possible classes of formation-water composition in different regions of the Gyda field have been identified by analysis of the produced-water data set. Anhydrite and barite precipitation are the two dominant mineral reactions taking place deep within the reservoir. Magnesium (Mg) stripping may be a result of multicomponent ion exchange (MIE), dolomite precipitation, or a combination of both. Reservoir temperature is lowered during coldwater injection. The solubility of anhydrite increases at lower temperature, and anhydrite will gradually dissolve in response to the movement of the temperature front, which is much slower than the formation/injection-water mixing front. The extent of mineral precipitation within the reservoir can be reduced by the heterogeneity; the modeling shows that the extent of ion stripping caused by mineral reactions in the reservoir is greatest when simulating a single uniform layer. Brine mixing and the occurrence of geochemical reactions caused by vertical mixing are not observable, even when assigning a high vertical permeability in a heterogeneous model.
Thermal modeling is included to evaluate the effect of nonisothermal processes and heat transport on the geochemical reactions, especially the anhydrite mineral reaction. We have investigated how the difference in horizontal permeability in the two layers affects brine mixing of formation and injection water and geochemical reactions.
The evidence from the produced brine chemistry suggests that the Gyda field has experienced a variety of geochemical reactions due to the high temperature and initial calcium concentration, and so it is worth reviewing the produced water dataset and studying what
Produced brine chemistry data from 16 wells in the Gyda field are plotted and analysed in combination with general geological information and the reservoir description. A one dimensional reactive transport model is developed to identify the possible geochemical reactions occurring within the reservoir triggered by seawater injection, then extended with the inclusion of thermal modelling and also to be a two dimensional vertical cross section model.
Three possible classes of formation water compositions in different regions of the Gyda field have been identified by analysis of the produced water dataset. Anhydrite and barite precipitation are the two dominant mineral reactions taking place deep within the reservoir. Magnesium stripping may be a result of multi-component ion exchange, dolomite precipitation or a combination of both. Reservoir temperature is lowered during cold water injection. The solubility of anhydrite increases at lower temperature, and anhydrite will gradually dissolve in response to the movement of the temperature front, which is much slower than the formation/injection water mixing front. The extent of mineral precipitation within the reservoir can be reduced by the heterogeneity; the modelling shows that the extent of ion stripping caused by mineral reactions in the reservoir is greatest when simulating a single uniform layer. Brine mixing and the occurrence of geochemical reactions due to vertical mixing are not observable, even when assigning a high vertical permeability in a heterogeneous model.
Thermal modelling is included to evaluate the effect of non-isothermal processes and heat transport on the geochemical reactions, especially the anhydrite mineral reaction. We have investigated how the difference in horizontal permeability in the two layers affects brine mixing of formation and injection water and geochemical reactions.
Advancements in horizontal-well drilling and multistage hydraulic fracturing have enabled economically viable gas production from tight formations. Reservoir-simulation models play an important role in the production forecasting and field-development planning. To enhance their predictive capabilities and to capture the uncertainties in model parameters, one should calibrate stochastic reservoir models to both geologic and flow observations.
In this paper, a novel approach to characterization and history matching of hydrocarbon production from a hydraulic-fractured shale is presented. This new methodology includes generating multiple discrete-fracture-network (DFN) models, upscaling the models for numerical multiphase-flow simulation, and updating the DFN-model parameters with dynamic-flow responses. First, measurements from hydraulic-fracture treatment, petrophysical interpretation, and in-situ stress data are used to estimate the initial probability distribution of hydraulic-fracture and induced-microfracture parameters, and multiple initial DFN models are generated. Next, the DFN models are upscaled into an equivalent continuum dual-porosity model with analytical techniques. The upscaled models are subjected to the flow simulation, and their production performances are compared with the actual responses. Finally, an assisted-history-matching algorithm is implemented to assess the uncertainties of the DFN-model parameters. Hydraulic-fracture parameters including half-length and transmissivity are updated, and the length, transmissivity, intensity, and spatial distribution of the induced fractures are also estimated.
The proposed methodology is applied to facilitate characterization of fracture parameters of a multifractured shale-gas well in the Horn River basin. Fracture parameters and stimulated reservoir volume (SRV) derived from the updated DFN models are in agreement with estimates from microseismic interpretation and rate-transient analysis. The key advantage of this integrated assisted-history-matching approach is that uncertainties in fracture parameters are represented by the multiple equally probable DFN models and their upscaled flow-simulation models, which honor the hard data and match the dynamic production history. This work highlights the significance of uncertainties in SRV and hydraulic-fracture parameters. It also provides insight into the value of microseismic data when integrated into a rigorous production-history-matching work flow.
Although the advantages of Low Salinity Waterflooding (LSW) have been widely reported, studies of LSW in the past two decades have mainly focused on the underlying mechanisms through core flooding experiments. For more successful and broader applications of LSW in the field scale, it is required to have a comprehensive understanding of the LSW performance with complex geological features on a large scale that has never been addressed in the past. This paper presents insights on field scale modeling and prediction of LSW to address the current challenges with: (1) an equation-of-state compositional simulator fully coupled to multiple ion exchanges, geochemical reactions, and wettability alteration; (2) incorporation of critical geological properties important in LSW; (3) effective closed-loop reservoir management for design and prediction of the LSW process; (4) LSW evaluation in a full field scale.
A mechanistic LSW model and a closed-loop modeling approach are introduced in this paper that can efficiently capture the critical effects of geology on the LSW process by integrating the use of geological software, a reservoir simulator and a robust optimizer. First, eighty geostatiscal realizations with different facies and lithology properties and distributions are generated to evaluate the effect of reservoir geology, in particular the critical effects of clay, on LSW. A wide range of recovery factors from 19% to 40% indicate that the effectiveness of LSW strongly depends on geological factors such as facies properties, clay distribution and clay proportion. In consistency with the laboratory and field-scale observations, wettability alteration has been identified as the dominant effect that contributes approximately 58% to 73% to the incremental oil recovery from these realizations. Detailed analyses of the key factors were addressed to allow the design of optimal injection strategies to maximize the oil recovery by LSW. LSW is then evaluated in a closed-loop reservoir management for a sandstone reservoir in both secondary and tertiary modes. It is found that secondary and tertiary LSW give about 6% and 4.1% incremental OOIP over high salinity waterflooding, respectively. The simulation results also indicate that the sooner the LSW process is started, the better the benefit is.
Holubnyak, Yevhen (Energy & Environmental Research Center) | Bremer, Jordan M. (Energy & Environmental Research Center) | Hamling, John A. (EERC at UND) | Huffman, Benjamin L. (Energy & Environmental Research Center) | Mibeck, Blaise (Energy & Environmental Research Center) | Klapperich, Ryan J. (Energy & Environmental Research Center) | Smith, Steven Alan (Energy & Environmental Research Center) | Sorensen, James Alan (U. of North Dakota) | Harju, John A. (Gas Technology Institute GTI)
The souring of oil (increasing concentrations of hydrogen sulfide [H2S] gas) from reservoirs in the Bakken Formation has been observed in the field. Souring of oil presents challenges including but not limited to health and environmental risks, corrosion of wellbore, added expense with regard to materials handling and pipeline equipment, and additional refinement requirements. As such, sour oil and gas have lower profit margin (~10% lower price) than traditional sweet Bakken crude.
The understanding of causes for souring in the Bakken Formation and its timely identification are essential for determining the best operational practices and mitigation procedures at this formation. This paper will present an outline of the research goals, a current understanding of souring at the Bakken, and initial findings. Over the course of this project, the series of case-oriented uncoupled compositional reservoir simulations were developed to research the most probable mechanism of H2S generation in the Bakken Formation. The results of this investigation will be correlated in the future with field data from the Bakken oil field operator and laboratory experiments.
Water injection is commonly employed to increase the average reservoir pressure and displace the oil. However, water flooding is not always successful. The most important problem is channeling of the injected water into high permeability zones which occur in heterogeneous reservoirs. This is particularly true in naturally fractured reservoirs.
Injecting low viscosity pH-triggered polymers into the reservoir to block the already swept fractures and high permeability zones is a promising solution. No injection of high viscosity gels or triggering agents is needed is this process. Polyacrylic acid microgels can swell a thousand fold as the pH of the surrounding solution changes, with an accompanying large increase in viscosity. In this paper we studied the factors affecting the feasibility and the placement of pH-triggered polymers into fractured reservoirs by performing several coreflood experiments in fractured cores.
Polymer treatment reduced the overall core permeability in all cases in contact with different minerals in various sandstone and carbonate fractured cores. At polymer concentrations of 1% or greater, the permeability reduction was more than a factor of ten. The polymer microgels showed excellent consistency after being one month in reservoir condition at 58°C and resisted flow at pressure gradients up to 80 psi/ft. The selection of polymer and salt concentration in polymer solution depends on the application and desired PRF value. However, the 1% polymer concentration and 3% NaCl concentration is recommended due to the ease of polymer preparation, injectivity, reasonable geochemical buffering time and PRF values.
Copyright 2008, Society of Petroleum Engineers This paper was prepared for presentation at the CIPC/SPE Gas Technology Symposium 2008 Joint Conference held in Calgary, Alberta, Canada, 16-19 June 2008. This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of SPE copyright.