Title: Fracturing Fluid Characterization Facility

Author: The University of Oklahoma

Sponsor: Gas Research Institute (GRI) and US Department of Energy (DOE)

Report Period: August 1991 -- December 1992 Annual Report

Objective: To report and discuss the progress made during the FFCF project's first full year of research and development. Technical Hydraulic fracture treatment design requires a myriad of system parameters.

Technical Perspective: Hydraulic fracture treatment design requires a myriad of system parameters. Many of these parameters are inherent properties of the reservoir to be hydraulically fractured. The fracturing fluid's flow and particle transport characteristics are important to this design process. The observations made in this research facility will closely relate to the flow behavior expected in an actual hydraulic fracture. These same observations can also be related to the more routine, practical fluid characterization techniques used by the industry.

Results: The prototype for a high pressure, high temperature (i.e., 1200 psig, 250 degrees F, parallel plate flow cell has been designed and constructed. An instrumentation and data acquisition system has been assembled that records temperature, pressure and velocity profiles of the fluid in the flow cell. A fiber optic based vision system has been incorporated. This novel system provides a low resolution optical image of the flow field that can be digitally recorded and analyzed.

Experimental work has been completed on im-permeable facings that serve as a replaceable lining for the walls of the flow cell. These facings are currently being fabricated using an epoxy resin. This resin system will be used later with an aggregate of silica particles to fabricate permeable facings. These permeable facings will be used in the study of fluid leaking off normal to the main direction of flow.

Preliminary experimental and numerical studies of fluid flow are reported. These studies aid in determining the minimum size requirements for fluid characterization experiments.

Technical Approach: The reaction frame, or mechanical body, of the flow cell was designed and constructed by MTS, one of the project's subcontractors. The functional requirements for this design were provided by the entire project group with input from the industry advisors.

The Electrical Engineering group at OU conceived and constructed the instrumentation and data acquisition system. The flow cell itself had to be designed to withstand the 1200 psig maximum working pressure (i.e., 12-MM lb.-force load). This requires a steel superstructure that inhibits any of the desired observations. Novel techniques of burying equi-spaced optical fibers in the facings to obtain a low resolution optical image of the flow field, imbedded optical glass windows that facilitate the use of laser-doppler velocimetry (LDV), and 3-D graphical representation of measured parameters such as pressure, velocity, and temperature make it possible to observe and analyze what would be impossible with conventional instrumentation.

Laboratory experiments and material property measurements all played a big part in selecting the epoxy resin as a facing material. Cement was initially thought to be the material of choice. Although it did exhibit some desirable physical properties, its mechanical integrity became uncontrollable as facings were actually fabricated.

Experimental and numerical research into turbulent flow and fluid leak-off have provided important information for understanding the application of the prototype. Limitations based on geometry are identified with these same techniques so future equipment and experiments for the FFCF can be designed and planned with clear objectives.

Project Implications: The research and development that has gone into the FFCF prototype will not only serve as the foundation for the future of this project but also provides the industry with valuable insight into some of the more fundamental aspects of fluid flow in a hydraulic fracture. These reports form the basis for advancing the state-of-the-art in rheology research for hydraulic fracturing.

Report Contents:

1.Introduction	10
Goals of the FFCF Project	10
Brief Description of the Proposed FFCF	11
The Flow Cell	11
Auxiliary Equipment	12
Instrumentation	12
Research and Development Plan for FFCF Prototype	15
Summary of Accomplishments	22
Analysis of Leak-off in Laminar Flow through a Porous Channel - Part I	22
Analysis of Leak-off in Laminar Flow through a Porous Channel - Part II	22
Heating FFCF Fluids by Heat Transfer from Warm Slot Walls	22
A Practical Phenomenology for Turbulent Jets of Polymer Solutions Discharged into Slots	23
An experimental Investigation of Jet Penetration into a Slot	24
Micro - Gas Permeameter	24
Evaluation of Cement as a facing Material	24
Data Acquisition and Control System for the FFCF Project	25
Halliburton Services	26
RE/SPEC Incorporated	27
MTS Systems Corporation	28
Summary of Additional Studies at OU	28
Viscoelastic Models	28
Viscoelastic Behavior of Hydroxypropyl Guar (HPG)	31
Retarded-Motion Expansion	31
Thin Domain Analysis	32
Miscellaneous Numerical Modeling in Progress	32
Bibliography	34
2. Analysis of Leak-off in Laminar Flow through a Porous Channel - Part I	37
Introduction	37
Problem Statement	37
Numerical Analysis	39
Discussions and Conclusions	43
Bibliography	44
3. Analysis of Leak-off in Laminar Flow through a Porous Channel - Part II	47
Introduction	47
Problem Statement	47
Numerical Analysis	50
Finite Difference Approximations	50
Numerical Results	51
Discussions and Conclusions	52
Bibliography	52
4. Heating FFCF Fluids by Heat Transfer from Warm Slot Walls	54
Introduction	54
The Analytic Solution	54
Numerical Solutions	55
Conclusions	59
Nomenclature	60
5. A Practical Phenomenology for Turbulent Jets of Polymer Solutions Discharged into Slots	61
Introduction	61
Formulation of the Problem	62
Semi-Analytical Analysis	64
Outline	64
Preliminary Goals	64
Basic Phenomenology	65
Basic Assumption	65
Models	65
Dynamical Equations	65
Prandtl's Mixing-Length Theory	67
Von Karman's Similarity Hypothesis	68
Velocity Profile	68
Turbulent Spread of the Mixing Zone I	70
Pressure Gradient	73
Mass and Momentum Integrals	74
Forward Mass Flux and Turbulent Penetration Length	75
Turbulent Spread of the Mixing Zone II	76
Forward Mass Flux and Velocities Results	80
Turbulent Penetration Length Results	88
Conclusions	91
Bibliography	91
6. An Experimental Investigation of Jet Penetration into a Slot	93
Introduction	93
Equipment	94
Slot Design	94
Support Equipment	95
The Fluids Tested	95
Reynolds Number for a Power Law Fluid	97
Results	98
Correlation	98
Estimation Penetration Lengths	105
Conclusions	105
Bibliography	106
7. Micro - Gas Permeameter	107
Introduction	107
Description	108
Theory	108
Operation	109
Equipment List	110
Calibration Procedure	111
Permeability Computations	115
8. Evaluation of Cement as a Facing Material	117
Introduction	117
Chemistry of Portland Cement	118
Materials Used	119
Sample Preparation Procedures	120
Mixing the Cement Slurry	120
Casting and Setting the Cement Slurry	120
Preparation of Core Plugs for Testing	120
Permeability Measurements	121
Cement Physical Properties	121
Permeability	121
Porosity	124
Uniaxial and Triaxial Compressive Tests	124
Beam Tests - Tensile Strength	128
Evaluation of Fluid Loss Characteristics in Cement Facings for FFCF	131
Water Extraction (Leaching) Tests on Set Cement	134
Results of Final Preparations of Facings	134
Conclusions	137
Bibliography	139
9. Data Acquisition and Control System for FFCF Project	140
Statement of the Problem	140
Laser Doppler Velocity (LDV) Measurements	140
Fiber Optic Pressure Transducers	142
Temperature Measurements	142
Fiber Optic Vision System	146
Data Acquisition	147
Performance Criteria	147
Benchmarks	148
10. Halliburton Services	150
Introduction	150
Overall Project Objective	150
Summary of Previous Work Performed in February 1991 to September1991	150
Objectives for October 1991 to September1992	151
Work Plan for October 1991 to September 1992	151
Work Completed During October 1991 to September 1992	152
Activity Plan for Verification Testing - Phase I	156
Description of Equipment	157
Test Matrix	159
Activity Plans for Verification Testing - Phase II	168
Research and Development Plans for FFCF Prototype	172
Fluid Behavior	172
Proppant Transport	180
Fluid Leak-off	185
Summary and Conclusion	191
11. RE/SPEC Incorporated	192
Introduction	192
Numerical Studies	192
Quality Assurance	197
Related Activities	199
Bibliography	200
12. MTS Systems Corporation	201
Introduction	201
Overall Project Objective	201
Summary of Previous Work	201
Specific Objectives	202
Work Plan for the Current Year	202
Work Actually Performed	203
Major Achievements	204
Major Technical Problems	204
Seal Test Report	205
Initial One Hole Seal Tests	205
One Hole Seal Tests at High Temperature	208