Artesian conditions in the Chilterns Chalk aquifer (North West of the London Basin) and the implications for surface water - groundwater interactions

The Chalk is a principal aquifer which provides an important resource in Southeast England. For two centuries, it allowed the establishment of a thriving watercress-growing industry, indirectly through diverted stream flow and directly, through the drilling of flowing artesian boreholes. The distribution of artesian boreholes across different catchments, suggests a regional control on vertical groundwater flow within the New Pit and Lewes Chalk units. Interrogation of location-specific information points to the confining role of a few key marls within the New Pit Chalk Formation, which can be traced up-catchment to where they naturally outcrop or have been exposed by quarrying. Evidence is found in geophysical logging of a number of boreholes across catchments, confirming a consistent pattern of the spatial distribution of such key markers. When tectonic stress was applied to the various Chalk Formations, the marl bands would have reacted producing more plastic deformation and less fractures in comparison with rigid rock strata. Such scenario would have created the conditions for secondary aquifer units, giving the Chalk confining or semi-confining hydraulic characteristics on a regional scale. This conceptual understanding helps explain the reasons that the river flow response to reductions in groundwater abstraction varies across the flow duration curve.

Aplicação da perfilagem geofísica na correlação estratigráfica de poços / Application of geophysical logging in the stratigraphic correlation of wells

A correlação estratigráfica de poços é de suma importância na indústria do petróleo. Ela tem como objetivo a determinação da continuidade lateral das rochas. A partir dela é possível definir estratégias de explotação de um campo petrolífero, bem como a continuidade do reservatório. Porém, a técnica da correlação estratigráfica não é uma tarefa fácil, e está sujeita a interpretações equivocadas, devido a variabilidade geológica e à ambiguidade das respostas das ferramentas de perfilagem. Com objetivo de melhor compreender e definir a continuidade lateral das camadas e dos reservatórios do Campo de Namorado, Bacia de Campos – RJ. Para isso foram selecionados três poços (NA45D, NA52D e NA49D) com dados de perfis de Raios Gama, Resistividade, Porosidade Neutrão e Densidade. Os perfis foram gerados através do software LogPlot e posteriormente interpretados. O intervalo do reservatório foi identificado em cada poço e correlacionado, o que possibilitou observar a continuidade do reservatório do Campo de Namorado e sua heterogeneidade.

Classification of Void Space Types in Fractured-Vuggy Carbonate Reservoir Using Geophysical Logging: A Case Study on the Sinian Dengying Formation of the Sichuan Basin, Southwest China

The fractured-vuggy carbonate reservoirs display strong heterogeneity and need to be classified into different types for specific characterization. In this study, a total of 134 cores from six drilled wells and six outcrops of the Deng #2 and Deng #4 members of the Dengying Formation (Sichuan Basin, Southwest China) were selected to investigate the petrographic characteristics of void spaces in the fractured-vuggy carbonate reservoirs. Four void space types (VSTs) were observed, namely the solution-filling type (SFT), cement-reducing type (CRT), solution-filling breccia type (SFBT) and solution-enlarging fractures and vugs type (SEFVT). The CRT void spaces presented the largest porosity and permeability, followed by the SEFVT, SFBT and SFT. The VSTs presented various logging responses and values, and based on these, an identification method of VSTs using Bayes discriminant analysis (BDA) was proposed. Two test wells were employed for the validation of the identification method, and the results show that there is good agreement between the identification results and core description. The vertical distribution of VSTs indicates that the SFT and SEFVT are well distributed in both the Deng #2 and Deng #4 members. The CRT is mainly found in the Deng #2 member, and the SFBT occurs in the top and middle of the Deng #4 member.

Study current oil-gas saturation according to the geophysical logging data in Pirallahi adasy field

The paper studies the current distribution of oil-gas saturation in the reservoirs of Kirmaki and Lower Kirmaki suits in Pirallahi adasy field according to the integral analysis using the results of field, geological, geophysical well logging, as well as those of laboratory investigations. For studying the heterogeneity of sections, the changes of reservoir parameters according to the logging data interpretation have been analyzed. Based on comparative analysis of data interpretation for old and new wells (PNNL and other logging measurements), the areas maintained productivity in research region have been revealed and the sites for new well drilling and residual oil extraction recommended as well.

Origin and evolution of unconformities in a continental rift basin: a case study from the Lishu Depression in Songliao Basin, China

A variety of unconformity types are commonly developed during the rifting of a continental basin. Identifying their origin and evolution is prerequisite to understanding the complex tectono-sedimentary evolution of the basin and to evaluate the basin’s oil and gas resources. Based on the 2D/3D seismic, geophysical logging, and subsurface lithological data, the unconformities within the rift layer of the Lishu Depression in the Songliao Basin are identified as disconformities, nonconformities and four ‘types’ of angular unconformities. Their evolution and origin are analyzed by associating the unconformities with the basin’s tectonic evolution. The results show that the rifting of the Lishu Depression was not a continuous process. Instead, several regional tectonic episodes influenced the basin’s evolution. Episodic compressional events and a phase of extension along the main faults determined the basin configuration and sedimentary fill characteristics of different sub-rifting stages. The tectonic history and related paleogeomorphology changes are the dominant factors in the formation of these different unconformity types. During the rifting process, the type and distribution of unconformity varied. In the initial rifting stage, the basin developed a nonconformity and four types of angular unconformities as the result of both regional uplift and fault block tilt. Rotation and tilting of the fault blocks during the intensive rifting resulted in two types of angular unconformities. Finally, in the recession rifting stage, a different form of angular unconformity and disconformity developed, mainly as a result of the regional uplift and subsequent subsidence.