天然气水合物作为一种非常规的清洁能源,在全球分布广、资源量大.自20世纪90年代以来,加拿大、美国、日本、中国已经先后进行了陆域及海域的水合物试采,但发现出砂、单井日产气量低、稳产时间短等问题,试采产量远不能满足商业化开发的需求,其中核心问题是对水合物开发过程中的相变、多相多组分多场耦合渗流特征的认识不够明晰.本文根据天然气水合物开发过程中涉及的渗流场、温度场、化学场、力学场等多场耦合特征,重点综述水合物生成/分解对各物理场主要特征参数的影响,包括水合物储层的孔隙度、水合物饱和度、渗透率、相对渗透率等基础物性参数及其动态演变,天然气水合物的导热系数、比热容、热扩散系数以及水合物生成/分解热等热力学参数,天然气水合物生成、分解动力学特征,纯水合物以及含水合物沉积物的力学性质等,最后阐述了天然气水合物开发渗流中的多场耦合关系及相互作用,提出了今后水合物开发多物理场特征及耦合渗流的科学研究、技术开发的有关建议.

As one kind of clean and widely distributed unconventional energy resource, natural gas hydrate (NGH) is attracting increasing attention these years. In this study, the methods of depressurization and thermal stimulation are adopted to dissociate the NGH experimentally, when the initial temperature is 1.0 °C, the initial pressure is 3.1 MPa, the porosity is 0.35 and initial NGH saturation is 32%. The results reveal that during the depressurization process, there exists a pressure difference threshold (ΔP = 0.19 MPa), and similarly a temperature difference threshold (ΔT = 1.4 °C) exists during the process of thermal stimulation. NGH will not dissociate until pressure difference or temperature difference outweighs the corresponding threshold value. In addition, the influencing factors of driving force on the gas production performance have been studied. When thermal stimulation is adopted, the driving force of the temperature difference will grow with the increasing hot-brine injection rate and the brine temperature, in which case the gas production rate will drive up. When depressurization is used, the pressure difference driving force will go up with the increasing depressurizing range and depressurizing rate. Driving force is a major factor during NGH dissociation by depressurization and thermal stimulation.

In order to inquire the laws of hot water flooding dissociation of natural gas hydrates in porous medium,experimental equipments on dissociation of natural gas hydrates have been design and laws on dissociation frontal brim of hydrates are inspected through thermal elect-dipole and resistance in these experiments.Results from massive experiments show that three steps characteristics(reservoir bed temperature rise,equal dissociation and frontal brim breach) are exhibited distinctly.In order to reveal substance of dissociation of natural gas hydrates,model on dissociation moving frontal brim of hydrates is built.Fit values and experimental values of temperature and electric resistance are analyzed contrast.It shows from fit values and experimental values that correlation express preferable,but more times of dissociation was needed for fit value than experimental value to break the dissociation frontal brim of natural gas hydrate.

A new one-dimensional experimental system for modeling natural gas hydrate(NGH) development has been designed to study the formation and dissociation process of NGH.In order to simulate the marine geological environment,NGH was made in a sand-packed tube,and then hot-brine was injected into the tube to study the thermal dissociation characteristics,and the injection parameters which will influence the thermal dissociation behavior and energy efficiency of NHG.The temperatures of the injected hot-brine were 60 ℃,80 ℃ and 100 ℃,and the injection rates 12 mL/min,15 mL/min and 18 mL/min respectively,and the time span for injection was 220 min to the maximum.The experimental results show that if the injection rate is fixed,the higher the temperature is,the larger releasing rate of gas from hydrate dissociation is and the lower energy efficiency becomes.Moreover;if the temperature of injected hot-brine is fixed,the higher the injection rate is,the larger releasing rate of gas from hydrate dissociation is and the lower energy efficiency becomes.As the injection time becomes longer,the energy efficiency of thermal stimulation decreases gradually.In this regard,the option of hot brine slug + water flooding at normal temperature,or the combination of the thermal method and depressurization were proposed in this paper to improve the economic efficiency to develop NGH reservoirs.

In order to investigate whether the combination of thermal stimulation and depressurization is propitious to natural gas hydrate(NGH) dissociation,experimental study was carried out by using a special-designed experimental system of NGH.NGH was formed artificially in a one-dimensional sand-packing tube.Then NGH dissociation experiment was performed by injecting hot-brine and then decreasing pressure(thermal stimulation plus depressurization).The change of temperature,resistivity,gas production rate and energy efficiency during the NGH dissociation were analyzed.Experimental results show that the process of gas production can be obviously divided into different stages.The temperature and resistivity change at measuring points reflects clearly the dynamic characteristics of NGH dissociation process.The comparison of energy efficiency from different methods shows that the energy efficiency is 1.8 when only thermal stimulation is used,and it increases to 2.88 when thermal stimulation is combined with depressurization.Above results indicate that thermal stimulation together with depressurization can achieve higher energy efficiency and is a better method for NGH dissociation.

Natural gas hydrate(NGH),as an alternative energy resource with huge potential,has attracted more and more attention in recent years.It is the basic work for the commercial development of natural gas hydrate reservoir to build a model to evaluate the quality of hydrate reservoir.Based on literature summarization and numerical simulation,the quality evaluation model of natural gas hydrate reservoir is built using the hierarchy fuzzy assessment,and the main parameters which influence the development effect are classified into different hierarchies and the weighting coefficients are assigned to these parameters in the assessment process.Finally,four natural gas hydrate reservoirs are analyzed which proved the validity of the evaluation model.

In order to apply physical simulation results to natural gas hydrate reservoir parameters to provide a theoretical framework for the design of a development plan, an analytical equation method was used to obtain the similarity criteria of natural gas hydrate reservoir development by physical simulation, based on a mathematical model of natural gas hydrate development. Given the approach of numerical simulation, a sensitivity analysis for all parameters was carried out, which specifically demonstrated that initial temperature is the most important parameter. Parameters of thermal conductivity coefficients are not necessary for conducting the NGH dissociation process, which will fundamentally simplify the design and establishment of the model. The analysis provides a sound theoretical basis and design principles for particular similarity.

A muhi-component mathematical model characterizing polymer enhanced foam flooding filtration is established with mass conservation principle of foam components. Considering combination of foam generation, coalescence and migration phenomena, the model effectively reflects mechanism of oil phase foam coalescence and polymer foam stabilizing. Differential numerical solution is conducted with adaptive implicit method. Validity of the mathematical model is verified with experiment. Meanwhile, taken foam flooding pilot region of a oilfield, a numerical simulator is employed to study filtration characteristics of enhanced foam flooding. It is indicated that the foam system could exist stably in the formation and gradually advance to production wells to improve oil recovery.

模拟地层多孔介质的条件,在填砂模型中进行了天然气水合物的合成和分解实验研究.本实验条件下,设定温度为1℃,水合物合成过程大约需要4 d时间,最后在压力为3 MPa左右时水合物稳定合成.从水合物合成过程的压力变化曲线可分析水合物成核及生长的过程,水合物分解采用逐步降压的方式.实验证明,水合物分解具有阶段性,当压力降至水合物稳定存在的相平衡压力后,水合物就完全分解;之后继续降压,产出气体均来自自由气的膨胀;降压分解时累计产气量的变化规律同普通油气藏的开采规律相似.

The scattered distribution of remaining oil and difficult to determine development potential are two major problems at ultra-high water cut stage.Aimed at the above-mentioned characteristics of reservoirs, on the basis of the statistics for the reservoir description and numerical simulation of typical reservoirs. Hierarchy division and weight analysis are carried out for the main factors influencing the distribution of remaining oil using AHP(Analytical Hierarchy Process)method.And the potential appraisai model of remaining oil for heterogeneous reservoir at high water cut stage is built.And then the appraisal sofeware of remaining oil for heterogeneous reservoir at high water cut stage is developed.The software is employed to successfully describe the remaining oil distribution in the same type reservoir of layer8 of block 21 in ShengTuo,providing guidance for scheming and implementation of unit adjustment.21 block 8 layer.

In view of the difficulty of describing the undulation detail of oil production by general prediction methods, grey topology prediction models of the oil production in different trends were established in this paper based on grey system theory. The process of the grey topology prediction of oil production in different trends in some oilfields in east China was introduced and the fluctuation shape of the future oil production curve was predicted accurately. The research suggests that the grey topology prediction model fits for the oil production prediction of such a fluctuation oilfield. The precision of the prediction values is very high. The basic rules must be determined before modeling, which include the trend,the exceptional way of obtaining the value at some periodic time,the time limit of continuous increasing or declining of oil production and so on. It is appropriate that the history period of used data in modeling is about 2 times longer than the prediction one.

There are problems to use the conventional producer fracturing forecasting model to petroleum engineering planning.Based on filtration theory and with the comprehensive consideration of the relative geologic parameters,production parameters and technology parameters,the fracturing response forecasting model is established for petroleum engineering planning.The sensitivity analysis is carried out to main parameters,such as treatment occasions,water cut of the fracturing zone,effective thickness of the fracturing zone,fracture conductivity and fracture length,under constant pressure production.The application results of 5 fracturing producers in Daqing oilfield indicate: this kind of model can meet the demand of petroleum engineering planning with high reliability and high accuracy.

使用自制的一维天然气水合物开采模拟实验装置,对天然气水合物降压开采进行了物理模拟实验研究,考察了降压幅度、降压速度对开采效果的影响.实验结果表明,降压幅度主要影响最终产出气体的总量,降压幅度越大,累积产气量百分比越大.降压速度越大,产气速率越高,当最终压力相同时,降压速度只影响开采持续时间,最终产气量百分比基本一致;降压速度越慢,当压力降到相同水平时累积产气量百分比越大,特别在降压初期这一现象更明显.

Aimed at the predicament of increasing difficulty in the oil field development, the attention of the oil companies has been turned to the management to achieve maximal benefit. The reservoir management has attracted extensive attention of reservoir engineers at home and abroad,whereas, the effective method of performance assessment is deficient and urgent. The balanced scorecard method including finance, growth, procedure and study/development is established with the combination of modern enterprise methods and the theory of reservoir management. It is indicated that the balanced scorecard can not only make the object determination of the reservoir management unit more comprehensively and perfectly, but also ensure the healthy development of the reservoir management unit through the object determination.

The gas production rate of thermal stimulation was mostly controlled by the changing of temperature field,that is to say,controlled by injection rate,water temperature and thermal properties of experimental model.Using the experimental system of natural gas hydrate(NGH) forming and production,the production behaviors of NGH by thermal stimulation were investigated.The heat loss of this thermal model is high so that the efficiencies of heat exchange and heat utilization are low.Under the experimental condition,the highest gas production efficiency is obtained by thermal stimulation when the water injection temperature is 81.44 ℃.According to the experimental data,the efficiency of heat exchange in actual NGH reservoirs can be up to 6,which indicates that production by thermal stimulation for NGH reservoir is feasible.Through a series of measures,such as optimizing temperature and rate of the water injection,applying hot water slug and normal temperature water drive,combining depressurization with thermal stimulation,lessening the heat loss in pipelines,the efficiency of thermal stimulation could be increased significantly.

Uncertainty of personnel's subjective cognition results in uncertainty in understanding the reservoir.After analyzing the cause of uncertainty in the process of oil-field development,the uncertainty problems in reservoir description,residual oil distribution,oil production prediction and plan of oil increscent measurement were taken as examples to show that uncertainty method is the key to solve those problems.Many uncertainty methods such as random modeling,fuzzy mathematics,mathematical statistics and optimization were introduced in the application of solving uncertainty problems in the oil-field development.

Aimed at the defaults of conventional interpretation method for inter-well tracer production curves,a new interpretation model for well-group tracer production curves was established.The objective function in the model is the minimization of match error for well-group tracer production curves,and the constraints include injection volume,area controlled by wells and others static and dynamic parameters.It is difficult to get partial derivative in least square fitting method,and the problem was avoided by using genetic algorithm to match the production curves.The automatic matching for tracer production curves was realized,and the solution speed and precision were improved.The application result shows reliability of the combination interpretation method.

The recovery mechanism was studied for the steam assisted gravity drainage(SAGD) process as a follow-up process after production by cyclic steam stimulation(CSS) in a medium deep and extra heavy oil reservoir using combined vertical injectors and horizontal producers.A high pressure and high temperature scaled physical model was used to study the formation and growth process of the steam chamber during SAGD experiment,with horizontal wells placed below the vertical wells at the offset distance.It is shown that the recovery mechanism is gradually transited to gravity drainage from an initial steam displacement after switching from CSS to SAGD.The entire recovery process can be divided into four stages,including preheating by steam stimulation,steam displacement,stabilized gravity drainage and depletion.A numerical simulation was conducted to optimize the well placement,well patterns and spacing,horizontal interval length,timing of switching to SAGD and operating parameters.A promising result was achieved from a field testing of this process in the extra heavy oil reservoirs of Du 84 block,Liaohe Oilfield.

Current profile control well selection has many influence factors and blindness problem,and some parameters are hard to record during actual operation.Constant weight method will lead to irrational result.Hence,fuzzy analytical hierarchy process on variable weight basis has been introduced.Each evaluation parameter of profile control is quantified based on 0.1～0.9 scale,fuzzy consistent matrix is established,the subordinate degree of each evaluation parameter of different block is optimized according to maximum subordinate degree principle,and these values of subordinate degree is finally combined to obtain the final result of each evaluation parameter.This method combines quantitative and qualitative analysis,eliminates the difficulty of expert weight distribution,and overcomes the drawback of constant weight method when lacking of some parameters.Case analysis result shows that this method can reduce the blindness in profile control well selection,make the decision result more scientific and reasonable,and is worth of spreading.

By performing core displacement and micro pore model displacement experiments,the mechanism and changing law of saliferous reservoir parameters were studied.The changing law of reservoir permeability was quantitatively described with the advanced method of support vector machine(SVM).The result shows that the changing law of saliferous reservoir parameters is a nonlinear relationship with several variables,and it is a very complicated process.There exists a critical value of permeability during the process of parameters change.With the displacement rate,pore volume of displacement and salinity increasing,the permeability increases when the permeability is larger than the critical value of permeability,and the permeability decreases when the permeability is smaller than the critical value of permeability.The quality of injection water has effect on the process of parameters change,and the final result is not affected.The dissolution of salt is the essential factors resulting in the change of reservoir parameters.The dissolution of dissoluble salt,existing as cementation,leads to the escape and migration of sand particulates,which is the direct reason leading to the change of reservoir parameters.