Mehdi Azari

Method and Application of Cyclic Well Testing With Production Logging

One of the predicaments of traditional well testing is the requirement of shutting-in a well to conduct a pressure buildup test for the purpose of obtaining well and reservoir properties. This deterrent factor is more prominent in prolific wells due to loss of revenue and problems associated with crossflow or when bringing a well back on production. Moreover, in case of commingled reservoirs, conventional buildup provides only average values of permeability, skin, and pressure. An innovative periodic well testing technique named WTPL (Well Testing by Production Logging) has been developed in which a cyclic wave function is imposed in the wellbore by modulating the flowrate. The analysis of the acquired rate function and the resulting pressure wave then provides formation characteristics such as permeability and skin in the vicinity of the well. This technique eliminates the disadvantage of shutting-in a well and maintains the production with a modulating periodic pattern. In addition, the WTPL can be easily applied to commingled reservoirs to estimate the individual permeability and skin for each layer. This effort has also resulted in the development of a downhole flow modulation tool capable of creating the cyclic flow patterns needed for the new testing method.

Fracturing Horizontal Wells in Gas Reservoirs

The fracturing of horizontal wells has recently gained wide acceptance as a viable completion option to maximize the return on investment. This is especially true in the case of tight gas formations. Horizontal wells have unique rock mechanics and operational aspects that affect fracture creation and propagation and control fracture orientation with respect to the horizontal well. The fracture orientation greatly affects the productivity and well testing aspects of the fractured horizontal wells. Depending on stress orientation relative to the wellbore, the fractures may be transverse or longitudinal. This paper presents a model for fractured horizontal wells operating under constant pressure conditions. This condition is most suitable for producing tight gas reservoirs. The model considers the presence of either transverse or longitudinal fractures. In this paper, we examine the factors involved in determining the optimum number of transverse fractures for both finite and infinite reservoirs. For a group of transverse fractures, the rate distribution for each fracture is presented and analyzed. The effect of uneven fracture length is briefly presented. The performance of a longitudinal fracture is examined and compared to a fractured vertical well and to a transverse-fractured horizontal well. A comparison of longitudinal versus transverse fractures from reservoir and operational points-of-view is presented. Also included is a short discussion of field examples. Because performance of a highly conductive longitudinal fracture is almost identical to that of a fractured vertical well, the existing solutions for fractured vertical wells may be applied to longitudinal fractures with a high degree of confidence. This approximation is valid for moderate to high dimensionless conductivity. In the case of transverse fractures, the outer fractures outperform the inner fractures. However, in most practical cases, more than two fractures are necessary to efficiently produce the reservoir. A simplified economic analysis supports this conclusion.

Review of Reservoir Engineering Aspects of Conformance Control Technology

Conformance control is any action taken to improve the injection or production profile of a well. It encompasses procedures that enhance recovery efficiency, improve wellbore/casing integrity, and satisfy environmental regulations. Unwanted fluid production in oil- and gasproducing wells is a limiting factor that controls the productive life of a well. The cost of produced water disposal in an environmentally non-threatening fashion may be a major concern for many producers. In addition, control of excess water and gas production improves profitability by allowing additional oil to be produced. Application of water control technology assists to minimize water production and maintain the oil flow rate of a well. Reservoir engineering and well testing play essential roles in characterizing and detecting the problems associated with producing formations and wells. This paper starts with problem identification in both producing and injection wells. It then covers the behavior and control of of several types of reservoirs with different drive mechanisms. Applications of reservoir simulation and well testing in the control of water and gas coning, determination of the amount and the best appropriate treatment application, effect of formation layering, control of relative permeability to water, application of permeability blocking agents, water channeling, secondary recovery, viscous fingering, and polymer flooding are detailed in this paper. In addition several techniques to evaluate the overall success of a conformance control procedure are presented.

New Well-Testing Methods for Rod-Pumping Oil Wells - Case Studies

A new well-testing method that provides high-resolution bottom-hole pressure (BHP) measurement has been developed for use with rod-pumping oilwell completions. This new well-testing technique is conducted by running a high-resolution downhole pressure gauge in a specially designed carrier assembly with the downhole pump. The gauge assembly is run on the rod string without pulling the completion packers or tubulars. With the new method, a downhole pressure system is in place while the well is flowing during the entire well test. High-resolution downhole pressure data can then be recorded during all flow and shut-in periods of the well test, providing more accurate pressure data and enhanced capability for reservoir analysis. Traditional techniques use wireline-conveyed pressure gauges, tubing-conveyed pressure-recording devices, and surface pressure-monitoring systems with an advanced fluid-level measurement to record data from pumping well completions. These methods are limited in their ability to provide accurate test results when low-pressure conditions prevail. The new method allows operators of low-pressure oilwell completions to use advanced well-test-analysis software to analyze actual pressure data to obtain reservoir properties and quantify skin damage. Data can be acquired from many types of rod-pump completions, including wells with downhole gas separators. Excellent pressure resolution has been obtained from this new testing technique with either of two downhole assembly designs depending upon the completion configuration. The results and the ensuing well-test analyses in several pilot pumping wells will illustrate that the new process permits more flexibility in well testing and allows for greater accuracy and better interpretation of data in low-pressure rod-pumping oil wells.

Design and Analysis of Fractured Horizontal Wells in Gas Reservoirs

Although horizontal wells may offer significant production improvement over vertical wells, it may be necessary to fracture horizontal wells to maximize their return on investment. This is especially true in the case of tight gas formations. This paper presents a model for fractured horizontal wells operating under constant pressure conditions, which is most suitable for producing tight gas reservoirs. The created fracture may be longitudinal or transverse. In this paper we examine the factors involved in determining the optimum number of transverse fractures for both finite and infinite reservoirs. For a group of transverse fractures, the rate distribution for each fracture is presented and analyzed. The effect of uneven fracture length is briefly presented. The performance of a longitudinal fracture is examined and compared to a fractured vertical well and to a transverse-fractured horizontal well. A comparison of longitudinal versus transverse fractures from reservoir and operational points-of-view is presented. Also included is a short discussion of field examples. Because performance of a longitudinal fracture is almost identical to that of a fractured vertical well, the existing solutions for fractured vertical wells may be applied to longitudinal fractures with a high degree of confidence. This approximation is valid for moderate to high dimensionless conductivity. In the case of transverse fractures, the outerfractures outperform the inner fractures. However, more than two fractures are necessary to efficiently produce the reservoir for most cases. A simplified economical analysis supports this conclusion.

New Well-Testing Methods for Rod-Pumping Oil Wells—Case Studies

A new well testing method that provides high-resolution bottomhole pressure measurement has been developed for use with rod pumping oil well completions. This new well testing technique is conducted by running a high-resolution downhole pressure gauge in a specially designed carrier assembly with the downhole pump. The gauge assembly is run on the rod string without pulling completion packers or tubulars. Using the new method, a downhole pressure system is in place while the well is flowing during the entire well test. High-resolution downhole pressure data can then be recorded during all flow and shut-in periods of the well test, which provides more accurate pressure data and enhanced capability for reservoir analysis. Traditional techniques use wireline-conveyed pressure gauges, tubing-conveyed pressure recording devices, and surface pressure monitoring systems with advanced fluid-level measurement to record data from pumping well completions. These methods are limited in their capability to provide accurate test results when low-pressure conditions prevail. The new method allows operators of low-pressure oil well completions to use advanced well-test analysis software to analyze actual pressure data to obtain reservoir properties and quantify skin damage. Data can be acquired from many types of rod-pump completions, including wells with downhole gas separators, Excellent pressure resolution has been obtained with this new testing technique using either of two downhole assembly designs, depending upon the completion configuration. The results and the ensuing well test analyses in several pilot pumping wells will illustrate that the new process permits more flexibility in well testing and allows for greater accuracy and better interpretation of data in low-pressure rod-pumping oilwells.

Well Testing and Evaluation of Tubing-Conveyed Extreme Overbalanced Perforating

Traditionally, underbalance perforating has been the preferred perforation technique. Recently, however, a new extreme overbalance perforating (EOBP) that has the potential to improve the completion efficiency of a well without additional stimulation has been introduced. With this method a well with a fluid column is pressurized with nitrogen to above fracturing pressure of the formation before the gun is fired. Gas is then injected, with or without acid or proppants, to create short fractures that extend from the perforation tunnels. The presence of gas lowers the amount of liquid that contacts with the formation, facilitates the wells coming into production after perforation, and results in less formation damage. This new EOBP method creates highly conductive short fractures, the benefits of which outweigh any restriction that may be caused by perforating debris. The debris that exits the gun when it detonates will be pushed away from the wellbore during the pumping stage, and this will greatly diminish any adverse effects on productivity that overbalanced perforating could cause. This can be considered as a near-wellbore stimulation method that also improves the completion efficiency of a well by allowing perforating and stimulation to be accomplished in one operation. By performing two or more completion procedures during a single trip into the wellbore, service operators have been able to generate economical advantages. There are numerous ways in which EOBP may be performed. This paper will cover the design, planning techniques, and equipment that can be used to perform tubing-conveyed overbalance perforating. Examples and field cases will show scenarios in which wells with a variety of wellbore conditions such as open perforations and packerless and tubingless installations can be perforated in an extremely overbalanced condition. An analysis technique that can be applied to a short falloff test immediately following the perforation treatment as well as the standard well testing is also described in this paper. The method of analysis can be used to calculate skin damage, formation permeability, reservoir pressure, and if applicable, fracture parameters such as fracture half-length and conductivity. Several field cases are included to illustrate application of this method.

Testing and Production Performance of Slim-Hole Wells

The petroleum industry is focusing on cost reduction and efficiency more than it ever had. Slim-hole drilling and completion technology offer significant cost reduction potentials to the oil and gas industry. To provide an insight into slim-hole technology, production, stimulation, conformance, perforation, and testing aspects of reservoirs with wellbore and completion string diameters of less than conventionally drilled and completed wells are detailed here. Productivity of both horizontal and vertical slim-hole wells, with and without hydraulic fractures, is compared with wells having standard wellbore sizes. Comparisons with conventional sized wellbores will be given that concern: (1) wellbore hydraulics, including nodal analysis and minimum gas rates required to lift fluids off the well, (2) the effect of wellbore diameter on transient pressure testing, and (3) coning and cresting problems. The performance of slim-hole wells compares favorably to standard wellbore completions for the parameters investigated in this study.