A Comprehensive Model of High-Rate Matrix Acid Stimulation for Long Horizontal Wells in Carbonate Reservoirs

A comprehensive model of high-rate matrix-acid stimulation for long horizontal wells in carbonate reservoirs: Part II-wellbore/reservoir coupled-flow modeling and field application

The analysis of well tests constitutes one of the most powerful tools for the effective description of a petroleum reservoir and its subsequent management. This requires that the well test be placed in the proper context of related disciplines, especially geoscience, production and reservoir engineering. Modern methods of automated data processing can conceal mathematical limitations and overlook the need for realistic physical and geologic models. This book emphasizes the plausible physical contexts and mathematical models and limitations, and also the importance of realistic geologic models in analysis. Scattered throughout the book are worked examples of the use of the methods described in the text. It also contains extensive appendices on permeability, application of Laplace transforms to flow equations valid for single and multi-layered systems, convolution and deconvolution, dimensionless parameters and P-theorems, and physical and thermodynamic properties of gases.

Fundamental and applied pressure analysis

it has been long recognized that in some reservoirs the flow does not follow the expected radial cylindrical pattern. Spherical flow may take place in systems with wells completed in thick reservoirs where a short completion interval is open to flow yielding a unique and more complex early-time pressure behavior. Some of the main reasons for partial penetration are to avoid coning of water and minimize sand production. A similar early-time pressure behavior may be due to the presence of plugged perforations. Such well completions are referred to as limited-entry, restricted-entry or partially penetrating wells. A typical case of spherical propagation of pressure transients occurs during the repeat formation tester measurements. Such a test measures spot formation pressures and recovers formation fluid samples for gaining an insight into the reservoir flow mechanics. The purpose of this study is to identify on the pressure and pressure derivative curves the unique characteristics for different flow regimes resulting from these type of completions and to determine various reservoir parameters, such as vertical, horizontal permeability, and various skin factors. The interpretation is performed using Tiab’s Direct Synthesis (TDS) Technique, introduced by Tiab (1993), which uses analytical equations obtained from characteristic lines and points found on the log-log plot of pressure and pressure derivative to determine permeability, skin and wellbore storage without using type-curve matching. The extension of this methodology for the case under study includes wellbore storage and skin effects. It is applied to both drawdown and buildup tests. We found that a spherical or hemispherical flow regime occurs prior to the radial flow regime whenever the penetration ratio of about 20%. A half-slope line on the pressure derivative is the unique characteristic identifying the presence of the spherical/hemispherical flow. The typical half-slope line of theses flow regimes is used to estimate spherical permeability and spherical skin values. These parameters are then used to estimate vertical permeability, anisotropy index and skin. Results of TDS technique where successufully compared to those of conventional technique for field and simulated examples.

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Determination of vertical and horizontal permeabilities for vertical oil and gas wells with partial completion and partial penetration using pressure and pressure derivative plots without type-curve matching

This paper presents a new spherical-flow cubic-analysis procedure for estimating horizontal and vertical permeabilities solely from pressure transient data acquired at an observation probe of the dual-packer-probe wireline formation testers (WFTs) for all inclination angles of the wellbore.

A Novel Analysis Procedure for Estimating Thickness-Independent Horizontal and Vertical Permeabilities From Pressure Data at an Observation Probe Acquired by Packer-Probe Wireline Formation Testers

K.K. Clark

Papers

Vertical Permeability From Limited Entry Flow Tests in Thick Formations