Investigating Horizontal-well Interference Test Applications
CHAPTER ONE
OBJECTIVES
The objectives of this study include:
- To investigate the existing interference test models and compare the solutions with alternative solution method used in this
- To examine the effects of multiple active wells on single horizontal observation well
- To study the influence of active well locations and distances on interference tests using horizontal wells
- To use field data and estimate the equivalent observation points for horizontal wells using existing
CHAPTER TWO
LITERATURE REVIEW
Well Testing
Tiab7 reported that the concept of analyzing pressure-time data from a producing or shut-in oil or gas well to obtain in-situ reservoir rock properties, such as permeability and porosity was first applied in 1933. Since 1933, hundreds of additional well test analysis technical papers have been published1. In 1967, Matthews and Russell2 published the first complete cohesive treatment of well testing and analysis. Till date, myriad of technical papers have been published on well test analysis. Earlougher1 defined pressure transient testing as generating and measuring pressure variation with time in wells, and subsequently, estimating rock, fluid and well properties. According to Tiab7, pressure transient testing has been extensively applied to determine heterogeneities (sealing faults, fractures, sudden change in rock characteristics such as permeability and porosity, etc) in petroleum reservoir systems, groundwater hydrology and other areas where the location of boundaries around a borehole is essential. Modern well testing has incorporated various well test techniques in horizontal wells for different reservoirs.
Review of Interference Testing in Horizontal Wells
Horizontal Wells: Definition and Objectives
During the last 40 years, it has been reported that advances in drilling technology have made it possible to drill horizontal. Interest, economics, publicity and technology have led a vast amount of research to be focused on horizontal wells in the last three decades. Drilling, completions, and reservoir engineering aspects of horizontal wells have received considerable attention8. Lacy et. al.9 defined horizontal wells from the operational standpoint as including all wells deviated above 70o to 75o from vertical, where conventional wireline tools cannot be used. From a reservoir standpoint, they stated that wells with deviations above 80o approach typical productivity of horizontal producers. Malekzadeh8 defines horizontal wells as “normally new wells, 1000 to 3000 feet long in the horizontal direction”. He stated that drainholes are generally drilled from the existing vertical wells and are 100 to 700 feet long in the horizontal direction. For the purpose of this study, horizontal wells refer to both the normal horizontal wells and the drainholes. Horne10 maintains that horizontal wells are now common in many different applications, making well test interpretations in horizontal wells important. According to his works, horizontal wells differ from vertical wells in the following ways, which are important in well testing:
- The open interval into which fluid enters the wellbore is very long
- Vertical permeability may play an important role, since there is likely to be considerable flow in the vertical
- There are number of different flow regimes during the transient test, however depending on the values of the reservoir parameters, one or more of the flow regimes may be 10 Authors 8, 11 have listed reservoir situations where horizontal wells are the most effective as:
- Tight reservoirs, especially if vertical fractures are suspected
- Naturally fractured reservoirs containing vertical fractures
- Unconventional low perme ability gas reservoirs
- Thin formations
- Thicker zones of marginal permeability
- Thin oil columns, especially when bottom water and/or gas cap is present
- Formations with gas or water coning problems
CHAPTER THREE
METHODOLOGY
The methodology of this study involves the application of a developed horizontal- well interference test model to field data.
The Horizontal-Well Interference Test Model
The horizontal-well interference test model developed by Al-Khamis et al.17, 21 have been used. In developing the model, the following assumptions were made: An anisotropic but homogeneous reservoir of uniform thickness in an infinite acting slab bounded at the top and bottom by no-flow boundaries. The flow is isothermal and single phase, and the fluid is of constant compressibility and viscosity. The initial pressure is assumed uniform. The flux in the horizontal well is also assumed uniform. The lengths of the horizontal wells were considered equal even though the model can work for unequal horizontal well lengths. The wells have non-uniform skin distributions and finite conductivity, but these effects have been shown to be negligible on observation well responses. Therefore, they were neglected. The effect of wellbore storage was also neglected for simplicity. It should be noted that observation-well responses may be influenced by skin effect when there is wellbore storage26. Horizontal wells may also be placed arbitrarily in the reservoir with respect to each other and within the pay zone.
CHAPTER FOUR
RESULTS AND DISCUSSION
Model Validation
The results obtained from model validation are presented in this chapter. The chapter also includes the application of the proposed methodology to field cases and the discussion of the results from field examples.
CHAPTER FIVE
CONCLUSIONS AND RECOMMENDATIONS
Summary and Conclusions
In this study, the interference testing using horizontal wells has been investigated. A model for horizontal well interference testing is presented. The model applies to homogeneous anisotropic reservoirs, and generates type curves for analysis of interference tests in horizontal wells. Interference test in the presence of multiple active horizontal wells has also been studied. This helps in understanding the effects of nearby active wells on the responses recorded during well tests. It is shown that the analysis methods used for single active horizontal well also apply to multiple-active horizontal wells. The results of this study show that the dimensionless pressure behavior at observation well is a function of well lengths, separation between wells (in x and y directions), horizontal directional permeabilities, number and locations of active wells. Wells separation distances in z-direction, however, do not influence pressure responses when the wells of interest are considerably far apart. Field data have been used to validate the model and the result of this study compares well with existing models. Analysis of pressure behavior of the field data indicate that pressure responses are very much in agreement with the type curves of this work.
Recommendation for Further Studies
It is recommended that the equations derived in this work be applied to:
- various reservoir systems such as finite, heterogeneous,
- pulse test models
Application of nonlinear parameter estimation by regression analysis to the field data is recommended in order to calculate reservoir properties such as storativity and transmissibility from the field data.
REFERENCES
- Earlougher, R. C. Jr.: Advances in Well Test Analysis, SPE Monograph Vol. 5, 1977.
- Matthews, C.S. and Russell, D.G. “Pressure Buildup and Flow Tests in Wells,” Society of Petroleum Engineers of AIME, New York,
- Ogbe, D. and Brigham, W.: “Pulse Testing With Wellbore Storage and Skin Effect,” SPE 12780, SPE Formation Evaluation, March
- Towler, B. F.: Fundamental Principles of Reservoir Engineering, SPE Textbook Series Vol. 8 (2002). Richardson,
- Guo, B., Lyons, W.C., and Ghalambor, A. Petroleum Production Engineering: A Computer-Assisted Approach, Elsevier Science & Technology Books,
- Lu, P. and Horne, R. N. “A Multiresolution Approach to Reservoir Parameter Estimation Using Wavelet Analysis,” paper SPE 62985 presented at the 2000 SPE Annual Technical Conference and Exhibition held in Dallas, Texas, 1–4 October .
