Background Information
Over the past decade, there has been shift to the exploration and production of Shale reservoirs in North America and this also represents a promising source of energy in many other countries around the world (Mickael, Barnett & Diab 2012). The two major technologies employed in the production of such reservoirs are the drilling of horizontal wells and hydraulic fracturing. In effect, commercial viability has a direct dependence on these operations.
An effective hydraulic fracture placement is one that provides maximum fluid conductivity and ensures wellbore stability through optimal number of fracture stages, propagation, geometry and maintenance of fracture geometry through the productive life of the reservoir. This requires zonal characterisation to obtain the petrophysical and geomechanical properties of the wellbore.
One major attribute of shale reservoirs that results in uncertainty in hydraulic fracture operation design is anisotropy. This is the directional variability in the permeability, rock strength and in-situ stresses around and along the wellbore. Two types of anisotropy are commonly observed in shale reservoirs, which are Horizontal Transverse Isotropy (HTI) and Vertical Transverse Isotropy (VTI). Adequate consideration of these two forms of anisotropy in the design of fracture placement will result in effectiveness and optimum productivity. The HTI anisotropy is usually stress induced and commonly available from traditional monopole log data gathered in the vertical section of the well.
However, the VTI anisotropy, which is intrinsic and dependent on the depositional nature of the shale, can only be obtained in the horizontal section of wells using wireline crosseddipole logging tool. Running of wireline tools in horizontal wellbores has proved complex and costly and is therefore not common practice (Mickael, Barnett & Diab 2012). This has resulted in information insufficiency in hydraulic fracture designs as this form of anisotropy has geomechanical implications The VTI anisotropy is used to characterize the brittleness of the reservoir which is a crucial property due to its direct impact on hydraulic fracture effectiveness (Amorocho, Langford & Mejia 2014).
As a result, there is a demand for routine access to VTI anisotropy evaluation in horizontal wellbores as erroneous fracture placement, due to insufficiency of information, leads to excessive well costs and reduced productivity. This is in direct response to the current quest in the industry for the reduction of uncertainty in fracture placement design and ultimately, production optimization of Shale reservoirs.
Rationale for Project Work
There is a demand for routine access to VTI anisotropy evaluation in horizontal wellbores as erroneous fracture placement, due to insufficiency of information, leads to excessive well costs and reduced productivity. This is in direct response to the current quest in the industry for the reduction of uncertainty in fracture placement design and ultimately, production optimization of Shale reservoirs.
Aim and Objectives
The aims of this project are to generate an effective optimization approach for fracture placement in anisotropic shale and also make an improvement on the understanding of the role of fracture placement in the optimization of shale reservoirs.
The project objectives are as follows:
1. Review and identification of the fundamental principles involved in fracture placement design.
2. Review of the concept of anisotropy, the geomechanical and petrophysical characteristics of shale reservoirs in which anisotropy is observed.
3. Investigation of the effects of anisotropy on hydraulic fracture pressure, geometry, propagation and post-fracturing operation wellbore stability.
4. Investigation of geomechanical and petrophysical evaluation of data obtained from azimuthal LWD sonic and spectral gamma gay tools.
5. Application of evaluation to data obtained from different shale reservoirs.
6. Integration of the results of numerical evaluations and software simulation. This will allow for the mapping of wellbores into various stress/ pressure zones, estimation of the number of fracture stages needed and zones to be fractured in order to obtain maximum productivity without impairing wellbore stability.
Methodology
The procedure for the execution of the project will start with an extensive research on the hydraulic fracturing, anisotropy in shale reservoirs and evaluation of images from azimuthal LWD sonic and spectral gamma gay tools. This will require review of previous related works and knowledge gathering via the library and internet. In addition, this will include acquisition of Shale reservoir evaluation images and data that have been obtained using azimuthal LWD Sonic and Spectral Gamma Ray logs from shale reservoirs such as Barnett, Marcellus and Fayetteville Shale from past papers.
Subsequently, these obtained images would be geomechanically and petrophysically evaluated. The geomechanical evaluation will involve dynamic stress and brittleness analysis for the computation of poisson’s ratio, young’s modulus, bulk modulus and shear modulus; while the petrophysical evaluation will involve obtaining the Total Organic Content (TOC), permeability and porosity. Mathematical models such as elastic moduli approach will be used to obtain a matrix of elastic constants from which the magnitude of anisotropy will be defined.
A simulation is then run on the obtained information from the analysis carried out. This will integrate all analysis and obtain numerically simulated hydraulic fractures with an optimal number of fracture stages, their location in the well and associated geometry. The simulation will be carried out using Petrel RE & Eclipse software.
Expected Contributions to Theory and Practice
Develop effective optimization approach for fracture placement in anisotropic shale and also make an improvement on the understanding of the role of fracture placement in the optimization of shale reservoirs.
Questions
1. Does the research involve, or does the information in the research relate to
(a) Individual human subjects
(b) Groups (e.g. families, communities, crowds)
(c) Organizations
(d) Animals?
(e) Genetically modified organisms
2. Will the research deal with information that is private or confidential? In the process of doing the research, is there any potential for harm to be done to, or costs to be imposed on:
(a) research participants?
(b) research subjects?
(c) you, as the researcher?
(d) third parties?
When the research is complete, could negative consequences follow: Yes No
(a) for research subjects
(b) or elsewhere?
3. Does the research require informed consent or approval from:
(a) research participants?
(b) research subjects?
(c) external bodies?
4. Are there reasons why research subjects may need safeguards or protection?
5. Does the research involve any “regulated work with children” and/or “regulated work with protected adults”, therefore requiring membership of the Protecting Vulnerable Groups (PVG) Scheme?
6. Are specified procedures or safeguards required for recording, management, or storage of data?
7. Does the research require you to give or make undertakings to research participants or subjects about the use of data?
8. Is the research likely to be affected by the relationship with a sponsor, funder or employer?
9. Are there any other ethical issues not covered by this form which you believe you should raise?
10. Does the research have potentially negative implications for the University?
11. Are any potential conflicts of interest likely to arise in the course of the research?
12. Are you satisfied that the student has engaged adequately with the ethical implications of the work?
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