Physical properties of sandstone reservoirs: Implication for fluid mobility

Core samples representing depths of hydrocarbon-bearing zones are not readily accessible for reservoir evaluations.On the other hand,wireline logs with incorporated seismic data,which can be archived over a more extended period while retaining their original forms,are typically more available for research purposes.Therefore,the study relies on wireline logs with seismic data to predict the reservoirs'fluid mobility by evaluating the hydraulic(flow)units,reservoir depths,fluid saturations,and geothermal gradients.It also indicates the associated water cut(C_(w))within Ritchie oil and gas field,Niger Delta considering a three-phase(oil-gas-water-bearing)reservoir(R_(A))and an oil-saturated reservoir(R_(B))delineated across three wells(R_(W1),R_(W2) and R_(W3)).Research activities combining the presented factors to achieve the stated objectives are not quite common within the study location.It shows lower,average and upper limits of the flow unit factors and irreducible water saturation(S_(wirr))within the reservoirs.The study shows the relationship between hydraulic units/fluid saturations and fluid mobility/associated C_(w) within the sandstone reservoirs.It maximises porosity(Ф)for the theoretical flow units'prediction during qualitative and quantitative estimation based on the adopted expressions.Therefore,the study reveals that water saturation(S_(w))and hydrocarbon/water ratios substantially control C_(w),and other contributing factors include thermal gradients and S_(wirr).The flow unit factors are also significant and will encourage fluid mobility.The evaluated reservoirs(R_(A) and R_(B))are below 10400 ft(3170 m)across wells R_(W1),R_(W2) and R_(W3) within the Agbada Formation of a geothermal gradient up to 2.7℃/100 m;therefore,they have good thermal conditions to enhance hydrocarbon mobility and increase S wirr.Hence,the reservoir should feature significant hydrocarbon extraction via primary recovery.The average water cut(C_(w-avg).)(12.3%)estimated for reservoir R_(A) is within the acceptable range;therefore,the associated water production from the three-phase reservoir will not be much of a concern.In addition,simple models are presented to aid an alternative approach for predicting reservoir quality and C_(w) within sandstone res-ervoirs,especially in the absence of core samples.

Investigation of the transformation of organic matter of carbonate deposits of the Semiluksky-Mendymsky horizon under hydrothermal conditions

The paper presents the results of studies on the transformation of the organic matter of siliceous-clayey carbonate rocks of the Semiluksko-Mendymsky horizon of the Romashkino oil field in a hydrothermal fluid for an hour(with a water-to-rock ratio of 33)at 340℃and 380℃and pressu res of 17 and 20 MPa.As a result of hydrothermal treatment,at 340℃and 17 MPa,based on nitrogen porosimetry and electron microscopy data,transformations of rock-forming minerals in the rock are observed.They lead to an increase in the volume and average diameter of mesopores in it and the formation of micropores,as well,which improve its filtration properties.At the same time,the amount of kerogen in the composition of the organic matter decreases and the yield of the petroleum hydrocarbon extract increases,in which,according to the SARA analysis,the content of asphaltenes increases and the content of resins,aromatic and saturated hydrocarbons decreases.In the composition of aroatic hydrocarbons,the proportion of a lkyltri methyl benzenes and dibenzothiophenes increases,phenanthrene homologues appear,and in the composition of saturated hydrocarbons,the amount of iso-structure alkanes decreases relative to the content of linear alkanes.Raising the temperature and pressure of the hydrothermal fluid to 380℃and 20 MPa increases the degree of kerogen conversion from 12.4%to 23.6%.At the same time,changes occurring in the component composition of petroleum hydrocarbon extracts remains similar to the experiments carried out at 340℃and 17 MPa;the content of naphthalenes decreases,the content of dibenzothiophenes increases and C_(11)-C_(17),C_(19)-C_(22)alkyltrimethylbenzenes appear.According to IR spectroscopy,with increasing temperature and pressure of the hydrothermal fluid the intensity of the absorption bands of the aromatic ring,aliphatic fragments,and oxygen-containing groups increases in resins;the structural-group composition of asphaltenes changes little:aromaticity and the content of condensed structures slightly increase.The revealed distinctive features in the composition of organic matter after hydrothermal impact on siliceous-clayey carbonate rocks confirm the concept of staged destruction of kerogen,when large structural heteroatomic blocks(asphaltenes)are split off at the initial stages.Changes occurring in the composition of petroleum hydrocarbon extracts indicate their involvement in the process of hydrothermal transformation of organic matter of siliceous-clayey carmbonate rocks with the predominant reactions of dehydrogenation of naphthenic compounds and oxidative polycondensation of aromatic structures.The data of electron microscopy and nitrogen porosimetry of rocks after hydrothermal exposure at 380℃and 20 MPa indicate a deterioration in their reservoir properties.The most optimal thermobaric conditions of the hydrothermal fluid for the generation of petroleum hydrocarbons from kerogen of siliceous-clayey carbonate deposits of the Semiluksko-Mendymsky horizon of the Romashkino field,which improve their reservoir properties,are 340℃and 17 MPa;with implication of hard-to-recover heavy hydrocarbon resources and wellestablished catalytic methods of in-situ conversion.