PROJECT OVERVIEW

Understanding and successfully predicting, characterizing, and modeling reservoir-scale structures are the aims of the PGRAC - PETROLEUM GEOMECHANICS RESEARCH AND APPLICATION CONSORTIUM. A key aspect of the program investigates mechanical processes and their interactions that affect hydrocarbon production from subsurface.

Geomechanical issues play acritical role on successful extraction of conventional and nonconventional hydrocarbon resources. Incorporating the effect of fractures into hydraulic fracturing treatment is difficult or impossible to characterize adequately using currently available technology. Consequently, stimulation of fractured shale and tight-sand reservoirs have been intractable to describe and interpret effectively, posing serious challenges for development, and accurate reservoir simulation and reservoir management. An integrated workflow for prediction and characterization of induced fracture networks holds great potential for enhancing production by increasing the success and efficiency of exploration and recovery processes.

Scope Of The Project

The scope of this project includes theoretical principles, practical modeling and laboratory verification of geomechanical models for hydraulic fracturing, wellbore integrity and injectivity problems in unconsolidated formations. The project

• creates and tests new mechanical models for failure of rock interfaces and cement interfaces which cannot be address with classical fracture mechanics

• develops new models for failure in unconsolidated formations to describe and predict channelization, water hammer and injectivity at water injectors in these reservoirs

• develops a workflow to assess and predict integrity problems along wellbore cement in water injector and wells subject to hydraulic fracturing stimulations

• designs new ways to incorporate microseismic and geological information for reverse modeling of fracture growth in naturally fractured reservoirs.

Our results and proposed workflows are applicable to different reservoirs and geological conditions. Ongoing studies include numerical, analytical and experimental research to deepen industry understanding of geomechanical processes involved in hydrocarbon production from subsurface.

Our research team comprises essentially from staff of the Craft and Hawkins Departments of Petroleum Engineering at Louisiana State University with the lead of Dr. Arash Dahi Taleghani. This group of petroleum and mechanical engineers depending on the theme of each specific task would work with other faculty members a wide range of skills in the departments of Geophysics, Mechanical engineering, Industrial engineering and Mathematics to conduct theoretical and experimental research.

We have collaborative research arrangements with Dr. Guoqiang Li (Mechanical Engineering), Dr. Bhaba Sarker (Industrial Engineering) and Dr. Yuri Antipov (Mathematics) to address different aspects of this multi-disciplinary research project. For geophysical aspects of the research we are cooperating with Dr. Juan Lorenzo. We are also proud of our graduate student staff helping us in this research project.

Our members are well aware of the challenges and questions facing exploration and development geoscientists and engineers. Our approach may seem theoretical and concerned with fundamental issues, but practical applications are central to our goals.

Current And Planned Research: Petroleum Geomechanics

Each year we will combine industry input with our own ongoing research plans to develop a set of key engineering research topics. We plan to continue research in several areas and effort on petroleum geomechanics and unconventionals.

Ongoing Research

Hydraulic Fracturing Modeling

In general, solutions for fluid-driven fractures are tremendously difficult to construct even for simple geometries. This difficulty is due to moving boundary conditions, non-linearity of the governing equation for fluid flow in fractures, the high gradient of displacement and pressure near the fracture tip, and non-locality of the solution. Non-linearity comes from the fact that fracture permeability is a cubic function of the fracture width. HF modeling efforts in this group are mainly focused around using extended finite element method to solve this problem. In this approach, discontinuities like fractures are allowed to propagate independently of the mesh configuration by permitting the discontinuity to cross the elements. For this purpose, finite element space will be enriched by additional functions which are inspired from the analytical or asymptotic solution of the problem. For instance, it makes it possible to embed discontinuities in the solution space. The enrichment is performed from node to node in a mesh by activating extra degrees of freedom when needed. XFEM intrinsic advantages make it an excellent candidate to tackle hydraulic fracturing problems, specifically in complex geometries such as fracture coalescence and fracture diversion.

Hydraulic Fracturing In Naturally Fractured Reservoirs

Hydraulic fracturing has been the most effective stimulating technique to augment recovery from shale gas reservoirs. Most of the time, the pre-existing natural fractures in these reservoirs are not capable of facilitating gas production prior to stimulation. The low conductivity of the natural fracture system could be caused by occluding cements. The fact that natural fractures might be sealed by cements does not mean that they can be ignored while designing well completion processes. Cemented natural fractures can still act as weak paths for fracture growth. Fault deformation processes and flow properties.

Integrated Analysis Of Hydraulic Fracturing Treatments

An integrated modeling methodology is proposed to predict the network of potential paths for hydraulic fracture growth in naturally fractured reservoirs based on formation properties and recorded microseismic maps. The generated network can be further used for forward fracturing simulations to determine the geometry and height growth of induced fractures, as well as proppant transports in the fracture network. Microseismic map is used to generate the network of pre-existing natural fractures to provide a more reliable map of induced fracture network. For different realizations of natural fracture distributions generated by computer simulations, cohesive interface technique is used to model the evolution of complex fracture networks.

Damage Mechanics For Rock

Following the exploration of new unconventional natural gas resources in the US, there has been a growing attention toward fracturing these formations as a proved methodology to augment gas production. Fracture treatments in the new discovered formations were always challenging as classic cap rocks become the target of stimulation treatments, which may endanger aquifers in case of severe height growth. The new plays and advance stimulation technology requires more sophisticated methods to model fractures behavior at the interfaces. Different approaches have been used in fracture mechanics to describe fracture behavior at the interface of dissimilar materials. Although, extensive research has been done in this subject in solid mechanics, this problem has not yet been explored in porous geomaterials. Poroelastic and poroplastic properties of rocks and the essential role of pore pressure on determining rock failure mechanism requires revisiting the theories proposed originally for the solids to adapt them for rocks.

To understand the constitutive behavior of the interfacial layer between shales and sands, we propose a set of lab experiments to obtain an interface fracture length versus loading curve and then to use it as a metric to investigate the robustness of different fracture mechanics techniques examined in this research. The Brazilian disk test, classic Brazilian test, and double cantilever beam test are among the candidate tests for this research. Dahi (2009) proposed a general linear fracture mechanics (LEFM) approach to incorporate the effect of discontinuities on the hydraulic fractures growth. In this approach, a new parameter has been introduced for the toughness of the discontinuities (cemented fractures or bedding planes). This model assumes a toughness value for the discontinuity. Considering the fact that lab experiments and outcrop studies have revealed formation of series of microcracks along failure paths inside the brittle material, the classical LEFM methods may not truly describe the physics of the failure, hence, we propose to examine non-linear fracture mechanics techniques to incorporate the effect of microcracks on the failure along the interface of two different rocks. Cohesive interface models and damage mechanics are two general venues to explore the nonlinear behavior of rock interface properties. We are developing physically consistent anisotropic continuum damage model (CDM) for the porous media, which incorporate elastic and plastic properties of rock. A user-defined subroutine will also be developed to implement this technique in a commercial finite element package (ABAQUS), hence it can be run with material anisotropy, dynamic problems, thermal stress and other available options for finite element analysis. This model can handle different sorts of discontinuities like bedding planes and natural fractures and their intersections in a single framework.

Drill Bit And Rock Interactions

Our research group is operating a unique experimental apparatus, called Single Cutter Machine, for drilling rock using PDC cutters under confining pressure to study drilling performance under different environmental conditions. In this research in addition to experimental studies, we utilize the results generate from the existing single Cutter apparatus to incorporate it into our mechanical damage models. We plan to use experiments to investigate the underlying fracture mechanisms of rocks to formulate a Continuum Damage Mechanics (CDM) based analysis framework, which considers several physical properties including rock anisotropic damaged properties, dynamic energy density, confining pressure and temperature effects. The proposed CDM scheme is already validated against a wide range of experimental data.

Leveraged Research

The Petroleum Geomechanics Research and Application Consortium leverages industry support through grants from Federal and State funding sources.

Underground Blowout

The proposed project seeks improvement in the environmental impact of shale gas resource development, which could be achieved by assessing issues related to wellbore integrity loss and gas migration that may lead to contamination of shallow groundwater resources and/or air pollution. On the other hand, there have been escalating concerns regarding aftermaths of hydraulic fracturing on wellbore integrity and drinking water pollution in the last couple of years that need to be addressed. An underground blowout is an uncontrolled flow of hydrocarbons from the blowout zone to a weaker zone within the same wellbore. In most cases, the influx fluid is contained in the subsurface formation receiving the flow; but in extreme cases, the flow will create a flow path to the surface completely outside the well. This scenario is typically remediable only by drilling a relief well at the bottom of the blowout well to achieve a kill. In a typical kick control operation, the well is controlled by restricting the fluid flow, which causes the pressure in the well to increase. If the pressure in the well reaches a threshold, failure of the cement sheath and the formation surrounding the well may occur, which may lead to underground blowout. One of the objectives of this project is to examine the likelihood of broaching or cratering resulting from underground blowouts during well control procedures in cases similar to the Deepwater Horizon. Key questions that will be addressed in this research are: Could loss of wellbore integrity at a given depth in a given well, i.e. fracture propagation from the wellbore, causes the fluid to flow through sediments to the sea floor? Does casing failure due to uncontrolled sand production and/or unsuccessful killhead procedures lead to an internal blowout? If it happens, what would be the probable complications for seafloor wellhead facilities? Moreover, wellbore integrity is also a crucial requirement for successful geological CO₂ sequestrations. The analytical solution proposed in this research will stand as a benchmark for numerical model developed to simulate this problem. The outcome could be used as a basis for well designs to substantially reduce the risk of having severe catastrophes resulting from underground blowouts in shallow and deepwater offshore drillings in Gulf of Mexico.

Zonal Fracture Propagation In Injectors

The economics of water flooding projects mainly depend on large injection rates with longer injectors’ life. Frac Packs are being used increasingly in poor consolidated sands to control sands and maintain high injectivity at the injectors. Additionally, due to larger temperature differences, most deepwater injection wells will exhibit some degrees of thermal fracturing. This fracturing might be beneficial in decreasing fracture gradient and consequently improving injectivity in the short term. In the long term however, it causes a drop in injectivity. Because of undesirable and expensive well intervention later during production, a clear understanding of the physics in the vicinity of injectors is crucial to reduce water flooding costs as well as increase injection efficiency.

Participation

Members of this consortium are anticipated to be oil and gas companies, service companies and investment Banks interested in the energy sectors. Companies participate in this Industrial Associates program through an annual subscription. Research results are shared equally among supporting companies at annual review meetings and through our private web site.

Research Planning and Reporting

Each year the annual research plan is discussed and approved by the Members. Our private Website is an important part of our information transfer strategy. The private side of the project Website will be launched by Fall 2015.

Mentoring And Case Studies

Interaction with the technical staff of our sponsoring companies allows us to test our concepts and methods on real problems while assisting sponsors in developing new reserves. Sponsors are encouraged to contact us with projects that could be mutually beneficial.

Timing

New members are welcome to join at any time. Founding member (joint by end of 2015) is exempt from joining fee.

Meeting Schedules

The annual Research Meeting is generally held sometime between late spring and early fall. The 2015 meeting will be held in New Orleans, in October. In addition, we can meet individually with Members either in Baton Rouge or at Members offices to discuss or review case studies or to provide background briefings or training for staff.

Contact Information

Arash Dahi Taleghani — Phone: (225) 578-6059

E-mail: a_dahi@lsu.edu