Effective porosity

About: Effective porosity is a research topic. Over the lifetime, 1199 publications have been published within this topic receiving 26511 citations.

Reservoir Characterization of Basal Sand Zone of Lower Goru Formation by Petrophysical Studies of Geophysical Logs

Abstract: The lower Indus basin is one of the largest hydrocarbon producing sedimentary basins in Pakistan. It is characterized by the presence of many hydrocarbon-bearing fields including clastic and carbonates proven reservoirs from the Cretaceous to the Eocene age. This study has been carried out in the Sanghar oil field to evaluate the hydrocarbon prospects of basal sand zone of lower Goru Formation of Cretaceous by using complete suite of geophysical logs of different wells. The analytical formation evaluation by using petrophysical studies and neutron-density crossplots unveils that litho-facies mainly comprising of sandstone. The hydrocarbons potentialities of the formation zone have been characterized through various isoparameteric maps such as gross reservoir and net pay thickness, net-to-gross ratio, total and effective porosity, shaliness, and water and hydrocarbons saturation. The evaluated petrophysical studies show that the reservoir has net pay zone of thickness range 5 to 10 m, net-togross ratio range of 0.17 to 0.75, effective porosity range of 07 to 12 %, shaliness range of 27 to 40 % and hydrocarbon saturation range of 12 to 31 %. However, in the net pay zone hydrocarbon saturation reaches up to 95%. The isoparametric charts of petrophysically derived parameters reveal the aerial distribution of hydrocarbons accumulation in basal sand unit of the lower Goru Formation which may be helpful for further exploration.

Determination of Shale Volume and Distribution Patterns and Effective Porosity from Well Log Data Based On Cross-Plot Approach for A Shaly Carbonate Gas Reservoir

Abstract: Determination of shale volume distribution is one of the most important factors that has to be considered in formation evaluation, since existence of shale reduces effective porosity and permeability of the reservoir. In this paper, shale volume and distribution (dispersed, laminar and structural) and formation effective porosity are estimated from well log data and cross-plots. Results show that distribution of shale is mainly dispersed with few of laminar ones, and the quality of reservoir (effective porosity) decreases with depth resulting in low productivity of gas wells drilled in lower zones. Good agreement of estimated shale volumes and effective porosities from neutron-density cross-plot with the values determined from gamma ray log (CGR) and core analysis demonstrates the accuracy and applicability of these plots in determination of petrophysical parameters from conventional log data.

The prediction of high porosity chalks in the East Hod Field

Abstract: The East Hod Field in the Norwegian Block 2/11 produces from the Lower Tertiary and Upper Cretaceous Chalk Group. Although at first sight the trapping mechanism of the East Hod Field appears to be structural, increased understanding of porosity preservation, combined with new seismic interpretation, demonstrates that there is also a strong stratigraphic component. Both autochthonous and allochthonous facies occur, the latter forming the principal reservoirs. The extremely homogeneous nature of the matrix means that variations in seismic response directly reflect changes in pore volume, and a good correlation between seismic impedance and porosity is observed. High quality 3D seismic data made it possible to undertake seismic inversion which, together with the correlation between seismic impedance and porosity, allows prediction of porosity variations within the inter-well volume. The results indicate that within the allochthonous reservoir units, porosity is maintained in down-flank areas at depths previously believed to be predominantly tight. Seismic inversion is particularly accurate for predicting porosity because of the exceptionally uniform nature of the chalk matrix.

Subsurface and Petrophysical Studies of Shaly-Sand Reservoir Targets in Apete Field, Niger Delta

Abstract: Conventional departures from Archie conditions for petrophysical attribute delineation include shaliness, fresh formation waters, thin-bed reservoirs, and combinations of these cases. If these departures are unrecognized, water saturation can be overestimated, and this can result in loss of opportunity. Wireline logs of four (4) wells from Apete field were studied to delineate petrophysical attributes of shaly-sand reservoirs in the field. Shale volume and porosities were calculated, water saturations were determined by the dual water model, and net pay was estimated using field-specific pay criteria. Ten sand units within the Agbada formation penetrated by the wells were delineated and correlated and their continuity was observed across the studied wells. The reservoirs had high volume of shale (Vcl), high hydrocarbon saturation, low water saturation, and good effective porosity ranging 12.50–46.90%, 54.00–98.39%, 1.61–46.0%, and 10.40–26.80%, respectively. The pay zones are relatively inhomogeneous reservoirs as revealed from the buckle’s plot except in Apete 05. The direction of deposition of the sands was thus inferred to be east west. Empirical relationships apply with variable levels of accuracy with observation of the porosity-depth, water saturation-depth, and water saturation-porosity trends. Core data is recommended for better characterization of these reservoirs.