A review of pressure transient analysis in reservoirs with natural fractures,vugs and/or caves

A review of the pressure transient analysis of flow in reservoirs having natural fractures,vugs and/or caves is presented to provide an insight into how much knowledge has been acquired about this phenomenon and to highlight the gaps still open for further research.A comparison-based approach is adopted which involved the review of works by several authors and identifying the limiting assumptions,model restrictions and applicability.Pressure transient analysis provides information to aid the identification of important features of reservoirs.It also provides an explanation to complex reservoir pressuredependent variations which have led to improved understanding and optimization of the reservoir dynamics.Pressure transient analysis techniques,however,have limitations as not all its models find application in naturally fractured and vuggy reservoirs as the flow dynamics differ considerably.Pollard’s model presented in 1953 provided the foundation for existing pressure transient analysis in these types of reservoirs,and since then,several authors have modified this basic model and come up with more accurate models to characterize the dynamic pressure behavior in reservoirs with natural fractures,vugs and/or caves,with most having inherent limitations.This paper summarizes what has been done,what knowledge is considered established and the gaps left to be researched on.

Effects of vugs on resistivity of vuggy carbonate reservoirs

The pore structure characteristic parameters of vuggy carbonate reservoirs were extracted,and matrix resistivity of vuggy reservoir was calculated by the percolation network simulation.A segmented cross-scale resistivity calculation method was established,in which the finite element method was used to simulate the resistivity of vuggy reservoirs.The mathematical models of vug porosity and water saturation with rock resistivity in vuggy carbonate reservoir were established,and the relationships between them were obtained.Experimental results verified the reliability of the simulation results.The method presented provides new technical means and research method for the resistivity log interpretation of vuggy carbonate reservoirs.The matrix porosity,vug porosity and matrix pore water saturation are the key factors determining the resistivity of reservoir rocks.

The Segmentation of FMI Image Based on 2-D Dyadic Wavelet Transform

A key aspect in extracting quantitative information from FMI logs is to segment the FMI image to get images of pores, vugs and fractures. A segmentation method based on the dyadic wavelet transform in 2-D is introduced in this paper. The first step is to find all the edge pixels of the FMI image using the 2-D wavelet transform. The second step is to calculate a segmentation threshold based on the average value of the edge pixels. Field data processing examples show that sub-images of vugs and fractures can be correctly separated from original FMI data continuously and automatically along the depth axis. The image segmentation lays the foundation for in-situ parameter calculation.

Automatic fracture–vug identification and extraction from electric imaging logging data based on path morphology

We present a path morphology method to separate total rock pore space into matrix, fractures and vugs and derive their pore structure spectrum. Thus, we can achieve fine pore evaluation in fracture–vug reservoirs based on electric imaging logging data. We automatically identify and extract fracture–vug information from the electric imaging images by adopting a path morphological operator that remains flexible enough to fit rectilinear and slightly curved structures because they are independent of the structuring element shape. The Otsu method was used to extract fracture–vug information from the background noise caused by the matrix. To accommodate the differences in scale and form of the different target regions,including fracture and vug path, operators with different lengths were selected for their recognition and extraction at the corresponding scale. Polynomial and elliptic functions are used to fit the extracted fractures and vugs, respectively, and the fracture–vug parameters are deduced from the fitted edge. Finally, test examples of numerical simulation data and several measured well data have been provided for the verification of the effectiveness and adaptability of the path morphology method in the application of electric imaging logging data processing. This also provides algorithm support for the fine evaluation of fracture–vug reservoirs.

零距离接触LPI

LPI(Linux Professional Institute，Linux专业协会)是一家按照Linux标准基础(LSB)的精神致力于标准化的、高质量的Linux认证的非盈利性机构。它作为中立于厂商的Linux培训和认证的主要提供商，专门负责界定中立于厂商和分销商的认证标准。该组织意识到，

Characteristics of Subaerial Karstification and Late Reconstruction in the Dengying Formation,Sichuan Basin,Southwestern China

Tectonic uplift at the end of Sinian resulted in the denudation of the Dengying （灯影） Formation on a different scale and the development of a great number of secondary dissolution vugs beneath the unconformity between Sinian and Cambrian.Geological and geochemical characteristics such as the development of caves,sinkholes,karst tubes and weathering crust,abrupt depletion and negative deflection of δ13C and δ18O in country rock and vug filling toward unconformity surface suggest that subaerial karstification is responsible for the development of secondary karst vugs within 150 m or so beneath the unconformity surface.This kind of secondary dissolution vug was partially or completely filled by different stage dolomite,calcite,quartz and bitumen during the later deep burial and uplift.Facts such as the obvious difference in δ13C and δ18O of the filling in the subaerial karst vug from the country rock and the value of δ13C and δ18O of the filling increasing or decreasing with that of the country rocks,suggest that the hydrothermal fluid charged in vugs is allogenic fluid.Subaerial karstification vug acted as a conduit for allogenic corrosive fluid which can create new secondary vugs and enlarge previous karst vugs.The dissolution,precipitant and recrystallization produced by allogenic corrosive fluid introduction and petroleum thermal cracking,caused contraction or enlargement of the subaerial karstification vugs and the development of new secondary vugs during the deep burial and uplift.The ultimate vug of deep burial dolomitite is determined not only by fluid charge,dissolution,mineral precipitant,and petroleum thermal cracking during the deep burial and tectonic uplift,but also by the amount of initial secondary dissolution vugs created by subaerial karstification.