Effects of Shear Fracture on In-depth Profile Modification of Weak Gels

Two sand packs were filled with fine glass beads and quartz sand respectively. The characteristics of crosslinked polymer flowing through the sand packs as well as the influence of shear fracture of porous media on the indepth profile modification of the weak gel generated from the crosslinked polymer were investigated. The results indicated that under the dynamic condition crosslinking reaction happened in both sand packs, and the weak gels in these two cases became small gel particles after water flooding. The differences were： the dynamic gelation time in the quartz sand pack was longer than that in the glass bead pack. Residual resistance factor （FRR） caused by the weak gel in the quartz sand pack was smaller than that in the glass bead pack. The weak gel became gel particles after being scoured by subsequent flood water. A weak gel with uniform apparent viscosity and sealing characteristics was generated in every part of the glass bead pack, which could not only move deeply into the sand pack but also seal the high capacity channels again when it reached the deep part. The weak gel performed in-depth profile modification in the glass bead pack, while in the quartz sand pack, the weak gel was concentrated with 100 cm from the entrance of the sand pack. When propelled by the subsequent flood water, the weak gel could move towards the deep part of the sand pack but then became tiny gel particles and could not effectively seal the high capacity channels there. The in-depth profile modification of the weak gel was very weak in the quartz sand pack. It was the shear fracture of porous media that mainly affected the properties and weakened the in-depth profile modification of the weak gel.

Depositional Environment of Es_4~u and Es_3~l Shales Based on Biomarkers from the Boxing Sag of Dongying Depression, East China

The Boxing Sag is located in the southwest of Dongying Depression, southern Bohai Bay Basin of East China. It is one of the main petroliferous sags in the Dongying Depression, and has two major source rocks, namely the upper 4th Member （Es4u） and lower 3rd Member （Es31） shales of Eocene Shahejie Formation, which are the new exploration targets in recent years. In this study, 16 core samples were collected from Es4u and Es31 shales in the Boxing Sag, and the saturate hydrocarbons were analyzed by gas chromatography （GC） and gas chromatography-mass spectrometry （GC-MS）, respectively. The results show that Es4u shale has obvious phytane and gammacerane predominance, higher concentration of tricyclic terpanes and regular steranes, and very low concentration of 4- methly steranes; Es31 shale has pristane predominance, lower concentration of tricyclic terpanes, gammacerane and regular steranes, and higher concentration of 4-methly steranes. The Es4u shale can be further divided into two types based on the distribution of n-alkanes in gas chromatograms： normal distribution and double peak pattern. The biomarker characteristics and sedimentary facies distribution show that Es4u shale was deposited in the saline-hypersaline semi-deep （Type A Es4u shale, sag center） to shallow （Type B Es4u shale, sag edge） lacustrine environments, Es31 shale was deposited in the freshwater-brackish semi-deep-deep lacustrine environments, and the former sedimentary facies maps of Es4u and Es31 in the Boxing Sag are further modified.

Coal-derived Gas Accumulation Characteristics and Exploration Prospects of Upper Paleozoic in Eastern Linqing Depression

1 Introduction Bohai Bay Basin is the highest oil production basin in China, but the proven reserves and production of natural gas is far less than the size of the oil. In recent years, petroleum geologists found one after another in Wenan Slope of Jizhong Depression, Kongxi and Wumaying buried hills of Huanghua Depression, Gubei-Bonan buried hill of Jiyang Depression, Wenliu buried hill of Dongpu Depression oil and gas from coal-bearing source rock of Upper Paleozoic. It shows that Upper Paleozoic of Bohai Bay Basin has good exploration prospects.

UNSTEADY FLOW OF NON-NEWTONIAN VISCO-ELASTIC FLUID IN DUAL-POROSITY MEDIA WITH THE FRACTIONAL DERIVATIVE

The fractional order derivative was introduced to the seepage flow research to establish the relaxation models of non-Newtonian viscoelastic fluids in dual porous media. The flow characteristics of non-Newtonian viscoelastic fluids through a dual porous medium were studied by using the Hankel transform, the discrete Laplace transform of sequential fractional derivatives and the generalized Mittag-Leffler function. Exact solutions were obtained for arbitrary fractional order derivative. The long-time and short-time asymptotic solutions for an infinite formation were also resulted. The pressure transient behavior of non-Newtonian viscoelastic fluids flow through an infinite dual porous media was studied by using Stehfest＇s inversion method of the numerical Laplace transform. It shows that the characteristics of the fluid flow are appreciably affected by the order of the fractional derivative.

THE PRESSURE TRANSIENT ANALYSIS OF DEFORMATION OF FRACTAL MEDIUM

The assumption of constant rock properties in pressure-transient analysis of stress-sensitive reservoirs can cause significant errors in the estimation of temporal and spatial variation of pressure. In this article, the pressure transient response of the fractal medium in stress-sensitive reservoirs was studied by using the self-similarity solution method and the regular perturbation method. The dependence of permeability on pore pressure makes the flow equation strongly nonlinear. The nonlinearities associated with the governing equation become weaker by using the logarithm transformation. The perturbation solutions for a constant pressure production and a constant rate production of a linear-source well were obtained by using the self-similarity solution method and the regular perturbation method in an infinitely large system, and inquire into the changing rule of pressure when the fractal and deformation parameters change. The plots of typical pressure curves were given in a few cases, and the results can be applied to well test analysis.

Basic characteristics and evaluation of shale oil reservoirs

Shale oil refers to liquid hydrocarbons existing in free,dissolved or adsorbed states in the effective source rock of mudstones or shales,where some residual oil is retained after hydrocarbon generation and expulsion from the mudstones or shales.Basically shale oil experiences no migration or only undergoes some primary,short-distance migration within the source rocks.So far,there is no consensus on the exact definition of shale oil in China.Researches on the reservoir-controlling factors and evaluation elements are also far from sufficient.In this study,shale oil reservoirs are defined as mudstones or shales excluding the interbedded or adjacent layers of coarser siliciclastic or chemical-biogenic lithofacies(e.g.siltstone,carbonate,salt or chert layers)in the source rocks.According to different reservoiring mechanisms,shale oil reservoirs are classified into“fracture type”and“matrix type”.The general features of shale oil reservoirs include:rich in organic matters,dominated by Type I and II_(1) kerogen(with Ro=0.6%-1.2%and total organic content(TOC)>2.0%),complex mineral compositions and laminated structures,tight storage space,low porosity and ultra-low permeability,and as well as the requirement for reservoir fracturing.This paper emphasizes the critical role of organic matter in the formation and evaluation of shale oil reservoirs,and its critical control on the oil generation potential and storage capacity of shale,which eventually determine the oil content and productivity of shale oil reservoirs.Besides,a set of reservoir evaluation criteria is also put forward with a focus on the TOC content,in which the threshold values of TOC are set to be 2%and 4%,and a variety of indicators are taken into account including the type and maturity of organic matter,the thickness of organic-rich shale,mineral compositions and rock types,porosity and permeability,and fracturing ability.The evaluation criteria divide shale oil reservoirs into three grades,i.e.,target reservoir,favorable reservoir and invalid reservoir.