Performance Model for Vertical Wells with Multi-stage Horizontal Hydraulic Fractures in Water Flooded Multilayer Reservoirs

For the characteristics of horizontal fractures in shallow low-permeability oil layers after hydraulic fracturing in multilayer reservoirs, horizontal fractures are taken equivalent to an elliptical cylinder with the reservoir thickness using the equivalent permeability model; then, upon the elliptic seepage theory, the seepage field which has led by a vertical well with horizontal fractures is divided into two parts: (1)radial flow from the external formation to the equivalent area of horizontal fracture and (2) elliptic flow in the equivalent area of horizontal fracture. The loss of pressure caused by threshold pressure gradient, material balance in the reservoir, and multi-well pressure superposition principle are synthesized to calculate the performance. Finally, separate-layer multi-stage horizontal fractured well performance is deduced by summing the performance of high-permeability oil layers and fractured thin low-permeability oil layers. Low-permeability thin oil layers in Xing Shu-Gang oilfield are taken as practical cases, and the well space limits and economic reservoir thickness limits are calculated by the performance model; the relationship among recovery and productivity intensity, and the ratio of thin low-permeability oil layers thickness to the total thickness are also discussed

New understanding on water-oil displacement efficiency in a high water-cut stage

Based on analyzing dominant internal and external factors affecting water-oil displacement efficiency, the variation of oil displacement efficiency is studied by means of experimental and theoretical analyses. Internal factors include reservoir heterogeneity (highlighted micro-pore structure heterogeneity) and wettability. External factors are waterflooding conditions, including pore volume (PV) of water injected, injection rate, and oil-water viscosity ratio. The variation mechanism is analyzed based on the definition, laboratory determination and field application of oil displacement efficiency. A viewpoint is proposed that the changes of wettability and pore structure in a high water-cut stage would reduce the critical capillary number and the residual oil saturation, leading to improvement of water displacement efficiency. More attention should be paid to water-oil displacement efficiency when water-flooding oilfield enters a high water-cut stage. Research on water-oil displacement efficiency must be deepened from three levels as follows: the first is the definition of laboratory values, the second is to study economic and effective conditions for getting (reaching) a certain oil displacement efficiency, the third is how to develop cost-effective techniques to improve the displacement efficiency by increasing capillary number. Key words: water-oil displacement efficiency, high water-cut stage, pore volume of water injected, critical capillary number, wettabilit

COUPLED NUMERICAL SIMULATION OF FRACTURING MULTILAYER RESERVOIR FLOW WITH LEAN-STRATIFIED WATER INJECTION

Many multilayer sandstone reservoirs have reached extreme high water content and high recovery stage after long time waterflooding. These inner LPTOLs have been the main potential reserves. Lean-stratified water injection is one of the most important technologies to increase production and develop potential for multilayer oilfields with extreme high water content. However, traditional models cannot entirely solve the inner boundary conditions of lean-stratified water injection. Therefore, we established the injection wellbore constraint equations, which were coupled with the oil/water two-phase numerical reservoir models. Upon an embedded fracture model for simulating hydraulic fractures, a method to simulate the reservoir with horizontal fractures is shown. The influences of reservoir and fluid, horizontal fractures, and injection-production characteristics are analyzed for oil production and water-content dynamic. Considering the specific situation of lean-stratified water injection wells, the influences of different segments numbers, modes of combination in segment layers, and rhythm characteristics of remaining oil reserves and distribution are evaluated

Skin aging associated with chromium among rural housewives in northern China

Previous studies have found associations between chromium exposure and skin damage. However, few studies have focused on both chromium and skin aging. This study aimed to assess the degree of skin aging symptoms and estimate the relationship between hair chromium and skin aging among rural housewives. We recruited 405 subjects in Shanxi Province of northern China and analyzed 397 eligible hair samples with inductively coupled plasma–mass spectrometry (ICP–MS). The subjects’ skin aging symptoms were assessed with SCINEXA™ (SCore of INtrinsic and EXtrinsic skin Aging). After adjusting for age and other important covariates, the regression results showed more severe skin aging symptoms in women with a higher level of hair chromium and presented an increasing linear trend. Vegetables, fruits, and beans might be a source of chromium exposure. We concluded that skin aging might be positively associated with hair chromium. It is necessary to take measures to reduce chromium exposure to prevent skin aging

Prediction of asphaltene precipitation during CO2 injection

Aimed at the possible phenomenon of asphaltene precipitation during CO2 injection, the equation of state established by Anderko was introduced to describe the phase behavior of precipitated asphaltene because of its strong polarity. The fugacity of the precipitated asphaltene component was derived and a calculation model of gas-liquid-asphaltene equilibrium was constructed. After matching of PVT experimental data from a reservoir, the model was used to calculate the volume of precipitated asphaltene during CO2 injection. The precipitation model suggests that for a constant injection pressure, the asphaltene precipitation first increases and then decreases as CO2 increases with the asphaltene precipitation reaching a maximum when the gas phase occurs in the system. When the CO2 mole percentage of the CO2-oil system is constant, the precipitated asphaltene reaches a maximum at the saturation pressure. 摘 要: 注入CO2提高原油采收率过程中可能出现沥青质固相沉淀。鉴于沉淀沥青质的强极性，采用Anderko建立的缔合混合物状态方程描述沥青质的相行为，并由此推导沉淀沥青质组分的逸度计算公式，建立注气过程中气-液-沥青质三相相平衡数值计算模型。以某油田实际原油为例，利用模型计算了CO2注入过程中沥青质沉淀量，结果与实验数据相近，表明沥青质沉淀预测模型具有一定的准确性。在此基础上，预测了注气过程中沥青质沉淀变化规律：注入压力一定的情况下，沥青质沉淀量随着注入CO2量增加呈现先增加后减小的趋势，当CO2-原油体系中出现气相时，沥青质沉淀量达到最大；当CO2-原油体系中CO2物质的量分数一定时，在泡点压力附近沥青质沉淀量达到最大。 Key words: CO2 flooding, asphaltene precipitation, fugacity calculation, phase behavior simulation, phase equilibrium calculatio

Association of Rare Earth Elements with Passive Smoking among Housewives in Shanxi Province, China

Background: Rare earth elements (REEs) are emerging contaminants. Previous studies reported the association between REEs and active smoking, but little is known about the effects of passive smoking on this condition. In China, female passive smoking is widespread, particularly in rural areas. Objective: This study aimed to estimate the relationship between REEs accumulation and passive smoking among rural housewives. Methods: We recruited 385 subjects in Shanxi Province of northern China, of whom 117 housewives were exposed to passive smoking, and 268 were not. We analyzed 15 REEs in the hair of housewives with ICP–MS, including lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and yttrium. Results: The results indicated higher levels of 14 REEs except for Sm in both the univariate and adjusted models among the housewives exposed to passive smoking. The increasing linear trend of adjusted odds ratios of 15 REEs supported their association. The Bayesian kernel machine regression (BKMR) models showed that 15 REEs had a significant overall effect, and Eu had a single-exposure effect with passive smoking. Conclusion: We concluded that passive smoking might be associated with increased exposure to REEs among rural housewives

Application of Lorenz-curve model to stratified water injection evaluation

To evaluate the effect of stratified water injection accurately during different development stages, a Lorenz-curve model was constructed upon a modified four-parameter Sarabia-Lorenz-curve model with water injectivity test data over years, and the relationship between accumulative perforated sandstone thickness and injected water volume of single wells was described by the model. Three evaluation indexes, dimensionless water injectivity intensity, vertical sweep efficiency and water-injection non-balanced degree, and their calculation were presented. Dimensionless water injectivity intensity is used to evaluate the distribution and balanced degree of water injectivity intensity, vertical sweep efficiency is the proportion of oil layers that produce oil, and water-injection non-balanced degree illustrates the overall water-injection balanced condition, then the model is solved by particle swarm optimization algorithm. Thirty-eight stratified water injection wells were evaluated in the Daqing Xingshugang oilfield. And the factors influencing the effect of water injection in single wells were studied considering segments construction, water allocation projects and reservoir physical properties. Finally, technological limits of stratified water injection were proposed under extreme high water-cut and recovery. Key words: stratified water injection, Lorenz-curve model, dimensionless water injectivity intensity, water-injection non-balanced degree, vertical sweep efficiency, technological limits of layerin

Zinc finger protein ZBTB20 is a key repressor of alpha-fetoprotein gene transcription in liver

The alpha-fetoprotein (AFP) gene is highly activated in fetal liver but is dramatically repressed shortly after birth. The mechanisms that underlie AFP transcriptional repression in postpartum liver are not well understood. AFP enhancer, repressor region, and promoter are implicated to be involved in AFP postnatal repression, but the major transcriptional repressor remains undefined. We previously identified a zinc finger protein gene ZBTB20. To determine its physiological functions in vivo, we have generated hepatocyte-specific ZBTB20 knockout mice by the Cre/loxP approach and demonstrated here that ZBTB20 ablation in liver led to dramatic derepression of the AFP gene in entire liver throughout adult life, although the hepatocytes were normally under nonproliferating status. Furthermore, we found that ZBTB20 was a transcriptional repressor capable of specifically inhibiting AFP promoter-driven transcriptional activity. Liver chromatin immunoprecipitation and mobility shift assays showed that ZBTB20 bound to AFP promoter directly. ZBTB20 was developmentally activated in liver after birth and inversely correlated with its AFP gene expression, suggesting that activated ZBTB20 expression in liver mediated AFP gene repression. Our data point to ZBTB20 as a key regulator governing AFP gene transcription and postulate a new model for the postnatal gene repression of AFP in liver