Table of Contents
Ridgeway Kite has built on its extensive experience in reservoir simulation solver techniques, and coupled this with the latest massively parallel computing systems to develop the 6X simulator. The resultant solution speed of 6X enables it to be adapted to more compute-intensive problems, specifically, to the implicitly coupled treatment of flow dynamics and geomechanics prevalent in the modeling of unconventional resources. This delivers a unique platform for unconventional field development planning, completion design and recovery management.
The full coupling of Geomechanical rock properties with the reservoir model allows the geomechanics of the reservoir to determine the shape, extent and conductive properties of each fracture stage, in each well, and the effect that fracturing has on existing or planned nearby wells.
Fractures – The image shows an example of the complexity generated by the rock breaking during hydraulic fracturing, showing both tensile & shear fractures.
The simulator models the life cycle of multi-well sections, from the fracturing of the first well, through to the end of production of the last well. It accounts for fracture generation, closure and well interference.
Calibrated models can be used to investigate the effects of well spacing, well timing, stage length, cluster spacing, job size, infill well location and design. These well plans can be further optimized using the integrated multiple realization capability in the simulator.
Optimizing well spacing – The image shows the interference between wells.
The 6X simulator has been designed to model unconventional oil and gas reservoirs. It includes features that have been developed for the CDOT (Completion Design and Optimization Tool) project with industry partners.
Through the project the simulator has acquired unique capabilities to help model the physics of unconventional reservoirs, including multi-porosity systems and vapor-liquid equilibrium in confined media. It includes advanced capabilities to help in modeling fracture mechanics above and beyond those found in other simulators and similar tools.
N-Porosity
6X has multi-porosity capabilities, in which different porosity systems (e.g. fractures, kerogen, sandstone) can be arbitrarily connected in a hierarchical model. They can be connected directly, in serial, or more generally as seen in the image above.
Multi Porosity – Illustration shows the variety of matrix-fracture connections possible in the simulator
Stress Dependent Permeabilities
Fracturing events are captured in 6X using regional tables of permeability modifiers versus net stress, which are applied dynamically to modify the reservoir flows. The table modifiers are either applied directly, or conditionally using a Mohr-Coulomb model and an input stress field. Several hysteresis models are also available to model the closing of fractures.
In addition, special consideration is given to the effects on well PIs and flows between different porosity systems, and provision is made to model background effects in nearby zones with transmissibility compressibilities.
6X uses the tracer facility in unconventionals for modeling the effects on flow of gels and proppants. Gels and gel breaker properties can be specified and their combined effect on fluid viscosity modulated. Proppant density can also be accounted for, with special consideration given to the prevention of ingress into non-fracture matrix, and to the differential flow of proppant in a fluid due to the effects of gravity.
Proppant – Example above with a cropped model displaying density of trapped proppant in a model (highest values in red).
Stress Shadowing – modelling the effect of well and stage spacing on the induced stress field
6X: Using the full stress tensor to predict stress shadowing
Stress shadowing occurs when the induced stress field from the hydraulic fracturing of one stage influences subsequent stages. For this to occur the stages need to be sufficiently close for the induced stress field to propagate to the next stage. The closer the stages the more pronounced the effect is likely to be.
To model stress shadowing the simulator needs to include a geomechanics model. It turns out that this model should solve at least for the normal stress tensor components, rather than just the hydrostatic mean stress. The 6X Simulator has this capability.
Solving only for mean stress
The simplest geomechanics model in 6X solves only for the average of the normal stress tensor components (the mean stress). Using this model for a single well study with close stage spacing we see no stress shadowing effect. The figure below shows the dynamic permeability induced by the fracturing of 8 consecutive stages. Clearly, each stage shows the same pattern of SRV generation regardless of the stress field generated by the previous stages.
To understand why this happens we plot the mean stress field along the path of the well just before the start of injection into stage 2.
The plot shows that the mean stress (red) is simply a multiple of the fracture pressure (blue) and matrix pressure (green). Since neither of these properties have significant values at the location of the second stage (dotted blue) there will be no stress shadowing effect modeled.
Solving for the full stress tensor
6X also has a more advanced geomechanics model, which can solve for each individual component of the stress tensor and use these values to predict the rock breakage in more detail. Using this model and plotting the normal stress tensor components along the well trajectory before the start of stage 2 we see an interesting effect.
The individual normal stress components are non-zero at the location of the next stage, despite the fact that they sum to zero, giving zero mean stress. Consequently we can expect stress shadowing effects when taking account of these components. The plot below shows the dynamic permeability, which clearly shows the influence of the stress field on subsequent stages.
Infill Wells – Manage spacing and timing while limiting fracture driven interactions
6X: Model pads to determine infill well spacing and bench development sequencing
Operators are focused on multi-well infill pad development programs to develop drill spacing units (DSUs) using fiscal discipline to generate free cash flow. Infill well design, spacing and timing become critical. Infill wells are impacted by the parent well pressure depletion and the associated change in the stress magnitude in the depleted drainage area.
Infill wells drilled offset to parent wells have experienced slurry loss during treatment due to fracture-to-fracture interactions between the infill and parent well hydraulic fractures. The change in stress magnitude leads to asymmetric fracture growth from the infill well into the depleted region of rock around the parent well.
These effects typically impair the performance of the infill well. Fracture driven interactions (FDIs) that lead to proppant reaching the parent well are detrimental, eroding pad production efficiency and value.
6X: Infill well spacing and timing to optimize for economic value through pad models
6X has the unique ability to model the changes in saturations, pressure and net mean stress simultaneously in one model. This capability can be used to optimize an infill well pad development program for multiple benches for a DSU. 6X captures the fracture driven interactions as the change in net mean stress is modeled through the infill well treatments and the depletion phase. The model dynamically captures the fracture opening; the propping at the end of the treatment; the compression of the fracture pore volume during depletion; and the loss of fracture conductivity with reservoir depletion. Stochastic multiple realization sensitivities can be performed using a single 6X license to assess the impact of treatment design on FDIs; the infill well count; spacing; the infill well timing; zippering and the impact of different operating strategies to understand and optimize the economic return on investment or net present value.
Example of interference on parent well from infill well
Ternary plot showing fracture to fracture interference
6X Infill Well and Pad Model Functionality:
- Optimize infill well spacing and timing
- Design selection: cluster spacing, clusters per stage and treatment volumes
- Hydraulic fracture treatment model including limited entry
- Dynamic stress change through hydraulic fracture treatment and depletion
- Proppant transport and proppant trapping model
- Fracture conductivity dynamically changes as hydraulic fractures are formed and close
- Infill well fracture driven interactions between infill and parent wells
Use 6X to optimize your infill well completion from stage treatment to multi-well pad optimization.
Well Completions – Optimize your well design for return on investment and well performance
6X: Modeling optimal stage design through multi-well DSU’s for value
With a highly reduced rig count, operators are completing previously drilled and uncompleted (DUC) wellbores with the goal of optimizing productivity and profitability by maximizing rate and minimizing cost. Stimulation designs remain focused on propping the fracture to maximize the conductivity and improve the well’s economic life by slowing the decline. The hydraulic fracturing of horizontal wellbores depends on both the rock properties and the completion treatment design and intensity. 6X is designed to model these for completions at any scale: from a cluster to a stage, from a well to a multi-well drill spacing unit (DSU).
Calibrate your model by history matching
Calibrate your model by history matching the parent well, then optimize the design of the child wells for performance and return on investment.
In 6X the fluid injection effects the net pressure in the rock, causing fractures to propagate and grow, defining the fracture height, width, length and hence the stimulated reservoir volume (SRV). Tracer modeling is used to capture the proppant transport, slickwater movement and leak-off. The unique Implicit Stress Solution models the dynamic change in mean stress and, once pumping is completed and the pressure distribution stabilizes, the compressibility controls the closure of the fractures and trapping of the proppant.
The decline in flow from the matrix to the fracture, and the decline in fracture conductivity with depletion, depend on the fracture closure parameters. Their impact on the parent well’s production and pressure may be used to tune the history match.
On completion of the history match, and having ascertained the reservoir character, multiple realization sensitivities of child infill well completion designs can be used to build a matrix of results. Return on investment (ROI) or net present value (NPV) can be correlated against effective fracture length and the number of stages, to determine the optimal value and performance scenario for wells in a particular DSU. This workflow should be used across multiple DSUs to reduce uncertainty and build the value.
6X Well Completion Functionality:
- Optimize parent to child well spacing
- Design selection: cluster spacing, clusters per stage and treatment volumes
- Limited entry perforation erosion
- Dynamic stress change through SRV stimulation and depletion
- Proppant and fluid pump schedule
- Proppant transport model and proppant trapping
- Fracture conductivity change as fractures open and close
Assess and optimize your well completion from stage treatment design to multi-well drill spacing unit optimization.
6X: Multiple Realizations – integral to every decision
Conventional and Unconventional Simulator with Fully Integrated Multiple Realizations (MR) capability
Quantification of uncertainty can be difficult and time consuming. Subsurface uncertainty exists from intrinsic geological complexity. A desire to quantify development options drives the successful application of Multiple Realizations; a pragmatic approach to optimize performance and maximize recovery from oil and gas reservoirs. It has successfully been applied from development appraisal stage projects to mature field projects and has increased project net present value.
6X Multiple Realization workflows
6X provides integrated functionality to create automated workflows performing hundreds of runs to quantify uncertainty in the following:
- Geological and fluid parameter sensitivities
- Experimental Design uncertainty quantification
- Assisted History Matching (AHM)
- Well and completion development selection
- Well and reservoir depletion forecasting
Unconventional reservoirs: well design to optimizing recovery
Many decisions are required to optimize recovery and economics from an unconventional well program. How many stages, how many clusters per stage, how much fluid and proppant to pump; how to determine the optimal well spacing and how many wells are required to develop a multi-bench drill spacing unit (DSU). A 6X Multiple Realization modeling workflow generates a range of outcomes to understand the hydraulic fracture growth and depletion to optimize EUR against net present value for a DSU.1
No hidden extras – a 6X license includes the MR module
The MR functionality exploits modern massively parallel architecture of 6X and runs on multi-CPU and multi-GPU systems. With the breakthrough and general availability of Cloud systems, clients can access 6X on Amazon AWS, Microsoft Azure and Google GCP.
Stimulated Reservoir Volume –
Understanding propped and unpropped fractures
6X: Modeling the Propped and Unpropped Stimulated Reservoir Volume
Hydraulic fracture designs continue to focus on increasing intensity to create larger stimulated reservoir volumes (SRV) through the combination of increasing proppant mass and fluid volume. With denser fracture distributions we see growth of multiple hydraulic fractures through bifurcation. The fracture distribution and hence shape of the SRV reflects reservoir heterogeneity as well as the stimulation design. Finer sand is typically pumped first followed by coarser sand, propping the created fracture geometry. Even so, many of the finer fractures and spatially distant fractures do not receive proppant and close unpropped. 6X models the unique opening, propping, closure and dynamic fracture conductivity for both the propped and unpropped fractures that form the SRV.
How do you assess your SRV in 6X?
The unique Implicit Stress Solution in 6X models the dynamic change in mean stress as a hydraulic fracture treatment is pumped. The simulator models the fracturing of the rock through the formation and subsequent propagation and growth of hydraulic fractures. Tracers are used to represent the fracturing fluid and proppant concentration in the hydraulic fractures. Fluid density, proppant density and bulk density control the proppant trapping resulting in a propped fracture; proppant gravity settling is modelled using the particle density. Should the propping criteria not be met, through insufficient proppant bulk density or the insufficient fracture width relative to the proppant particle diameter, the fracture remains stimulated but unpropped.
6X tracks the propped and unpropped hydraulic fractures that form the SRV. The user will see a hit from a child well on a parent in the form of a pressure pulse that has passed through the SRV.
Once pumping is completed, and the pressure distribution stabilizes, the rock compressibility model causes closure of the fractures. A propped fracture will maintain significant fracture conductivity. In comparison, an unpropped fracture will close quickly and will have minimal, fracture conductivity.
On completion of the treatment schedule, a production forecast can be run. The net stress increase is modeled as the reservoir depletes and the fractures continue to close with time. The model can be calibrated to observed data, and different SRVs evaluated.
6X Stimulated Reservoir Volume Parameters:
- Dynamic stress change through SRV stimulation and depletion
- Proppant and fluid pump schedule
- Proppant transport model and proppant trapping
- Fracture conductivity change as fractures open and close
Optimize SRV size and propped volume adjusting cluster spacing, clusters per stage and design volumes
Extreme Limited Entry: A Well Design Application to Reduce Stage Count
6X: Modelling Extreme Limited Entry Completions to Reduce Stage Count
Extreme Limited Entry designed wells can improve the distribution of completion fluid and proppant across clusters. The combination of limiting the number of perforations per cluster and designing with step increases in slurry rate to maintain sufficient treatment pressure to overcome
the perforation friction pressure drop enables treatment of all the clusters from the heel to the tow of a stage. This design in turn the allows the stage length to be increased while maintaining cluster efficiency.
How can you design an Extreme Limited Entry completion with 6X?
The 6X completion model incorporates the Bernoulli perforation flow model to describe the pressure drop across a perforation.
Perforation erosion leads to an increase in perforation diameter during the pumping of the fluid and proppant. While erosion occurs at a slow rate, photography has shown that it can be significant. The simulator models erosion as a dynamic increase in perforation diameter and it is based on correlations from field and laboratory observations. The perforation diameter is time dependent; it is a function of proppant size and concentration
in the completion fluid, fluid rate and an erosion rate. As the perforation diameter grows, the pressure drop across the perforation decreases resulting in the perforation taking a reduced fluid and proppant volume. Increasing the slurry rate while pumping maintains sufficient pressure in the wellbore above the perforation friction drop pressure enabling treatment all the way to the toe cluster, despite the perforation erosion.
Combine this with 6X’s unique Implicit Stress Solution that models the stress change as the completion is pumped. The simulator models the cluster entry pressure, the fracture initiation pressure, the stress increase and the fracture growth at each cluster as the completion is pumped.
Once the pumping schedule is complete, a production forecast can be run. The stress decrease is modeled as the reservoir depletes and the fracture closes. The model may be calibrated to observed data. Perforation size and cluster spacing can be optimized, and in turn designed stage length increased.
6X Extreme Limited Entry Design Parameters:
- Design perforation size, select proppant and fluid
- Design cluster locations with limited entry perforations
- Optimize fluid pump schedule to ensure fracture entry pressure is attained for all clusters in the presence of erosion
- Assess dynamic stress changes for the life of wells
Optimize cluster spacing, clusters per stage and design a well with reduced stage spacing
6X: Fully Integrated Multiple Realizations
Quantification of uncertainty can be difficult and time consuming. Subsurface uncertainty exists from intrinsic geological complexity. A desire to quantify development options drives the successful application of Multiple Realizations (MR); a pragmatic approach to optimize performance and maximize recovery from oil and gas reservoirs. It has successfully been applied from development appraisal stage projects to mature field projects and has increased project net present value.
6X Multiple Realization workflows
6X provides integrated functionality to create automated workflows performing hundreds of runs to quantify uncertainty in the following:
- Geological and fluid parameter sensitivities
- Experimental Design uncertainty quantification
- Assisted History Matching (AHM)
- Well and completion development selection
- Well and reservoir depletion forecasting
Unconventional reservoirs: well design to optimizing recovery
Many decisions are required to optimize recovery and economics from an unconventional well program. How may stages, how many clusters per stage, how much fluid and proppant to pump; how to determine the optimal well spacing and how many wells are required to develop a multi-bench drill spacing unit (DSU). A 6X Multiple Realization modeling workflow generates a range of outcomes to understand the hydraulic fracture growth and depletion to optimize EUR against net present value for a DSU.
No hidden extras – a 6X license includes the MR module
The Multiple Realizations functionality exploits modern massively parallel architecture of 6X and runs on multi-CPU and multi-GPU systems. With the breakthrough and general availability of Cloud systems, clients can access 6X on Amazon AWS, Microsoft Azure and Google GCP.
Together at Last: Geomechanics, Hydraulic Fracturing and Flow Simulation in a Fully Integrated Model
Simulate Your Multi-Well Unconventional Workflows from Pumping Schedule to Reservoir Depletion in 6X
A unique approach that incorporates both fracture creation and depletion in one model
6X is a fully featured, multi component numerical reservoir simulator. The model incorporates the physics required to capture the hydraulic fracturing and production periods. Engineers can determine how fractures are created, induced and close evaluating their impact on a well’s production and the production of neighboring wells.
Capturing the complexity of hydraulic fractures and the dynamic changes within those fractures as fluid and proppant are injected and produced is difficult to do accurately. The legacy approach is to use two applications: (1) design the hydraulically fractured completion, (2) model the production with a flow simulator. To create an accurate representa- tion of the hydraulic fracture and the production flow, the 6X simulator integrates the hydraulic fracturing and fluid flow into one model. This functionality enables the modeling of the whole lifecycle of a multi-well drilling spacing unit (DSU).
Understand and explore unconventional reservoir development opportunities in 6X
6X enables engineers to more accurately, consistently and rapidly investigate:
- Infill well locations and infill well timing
- Dynamic stress changes from hydraulic fracturing, depletion and infill wells
- Proppant transport and tracking
- Re-fracture completion designs
- Huff-and-puff EOR gas injection process
Power, accuracy, and flexibility at your fingertips
6X has an extensible architecture enabling it to run on CPUs, GPUs or on the Cloud to achieve fast turnaround times modeling multi-well scenarios.
Input pumping schedule
Input the detailed pumping schedule for each stage.
Fracture creation including geomechanics
Create tensile and shear fractures with an implicit stress or geomechanics solution.
Calibrate to observed data
Match simulated results with observed data. See the impact of ‘fracture hits’ from new wells in older wells.
Consistency in one model
Add infill wells and pumping schedules, create hydraulic fractures and calibrate to observed data. Finally, run forecast sensitivities.
6X: Solving Challenging Problems Fast
Conventional and Unconventional Simulator with Fully Integrated Geomechanics
Conventional and Unconventional reservoirs, from structurally simple to geologically com- plex, can be modeled with 6X in Black Oil or Compositional mode.
6X provides unique functionality including:
- Assisted History Matching (AHM) and uncertainty analysis with integrated multiple realizations
- Unconventional reservoir modeling with a multi porosity planar fracture solution for efficiency
- Proppant and fluid pump schedules; proppant transport and tracking
- Hydraulic fracturing and a dynamic geomechanical stress solution
- Development optimization
- Discretized wells
- Scripting
- Massively parallel extensible architecture
For Unconventional reservoirs, 6X models the life cycle of multi-well DSU; from the fracturing of the first well through to the end of production of the last well. The model accounts for fracture generation, closure and well interference.
6X is a single model is used for both the hydraulic fracturing and depletion periods. Incorporating the physics for the dynamic geomechanical stress change, the model captures the impact of infill wells on parent wells enabling the user to match observed data and evaluate different development scenarios including: Well place- ment, well spacing, well timing, completion design, proppant and fluid placement, re-frac- turing and huff-and-puff EOR gas injection.
The modern design of 6X delivers consistent results across all platforms whether running on multi-CPU, multi-GPU or Cloud systems.
Re-fracturing: Optimize Re-fracture Design to Maximize Drainage
Modeling Re-fracture and Infill Wells to Maximize Drainage and Avoid Asymmetric Fractures
Re-fracturing a well has two primary benefits: (i) Providing incremental production from a well with an early generation completion by re-fracturing with tighter cluster spacing; (ii) Elevating stress and pressure prior to fracturing an adjacent infill well to prevent EUR loss due to asymmetric fracture growth.
How can you design re-fracture well programs to maximize well economics?
6X uniquely incorporates the stress change from fracture creation and reservoir depletion in one model. The simulator models the stress increase and decrease of the initial completion execution and subsequent depletion; Also, the stress increase of the re-fracture and infill well completions followed by the stress decrease as the wells deplete.
With the Implicit Stress Solution, the above model shows virgin pressure between the original clusters. [The rock must be hydraulically re-fractured to produce.]
Assess and optimize your refracture design to improve well performance, model stress changes and design adjacent infill wells to avoid asymmetrical fractures and maximize reservoir drainage. Validate historical stress and well performance to assess new re-fracture opportunities using cemented or an expandable liner combined with extreme limited entry. Evaluate improved cluster efficiency to increase well EUR and maximize drainage.
6X – Re-fracture Design Parameters:
- Assess dynamic stress changes for the life of wells
- Design re-fracture cluster locations with limited entry perforations
- Optimize adjacent well design to avoid asymmetrical fractures
- Optimize proppant and fluid pump schedule per stage
In a recently published field test by an operator, 6X confirmed that incremental oil production increased by 32% over a 6-month forecast after re-fracturing a well.
Proppant Optimization: Sizing Your Treatment To Maximize Well Economics
Simulate your Wells from Proppant and Fluid Pumping to Reservoir Depletion in 6X
Proppant selection, proppant concentration and the pump schedule are key design parameters for well hydraulic fracture treatments.
In recent years, in attempting to increase production, operators have increased the proppant concentration and the fluid volume pumped. Fracturing fluids have evolved from gel-fracs to slickwater fracs, recently with high-viscosity friction reducers (HVFR) and operators are pumping cheaper regional sand in order to reduce costs.
So how can you optimize your treatment size to maximize well economics?
6X uniquely incorporates fracture creation and reservoir depletion in one model. It can model production forecast sensitivities over a range of proppant concentrations for economic evaluation and design optimization.
Physics for Proppant Transport:
- Models for particle settling
- Tortuosity modifiers for complex fractures
- Fluid viscosity modeling, including breakers
Proppant and Fluid Design Parameters:
- Proppant type and fluid type
- Proppant concentration and fluid volume per stage
- Proppant and fluid pump schedule per stage
History Matching Well Hydraulic Fracture Treatments:
- Pressure and rate match for injection and production phases
- Proppant and fluid tracers by stage for tracking and flowback
- Propped, SRV and fracture-matrix connection
- Dynamic stress changes due to pumping and depletion
