Low Permeability Oilfield Research Articles

New Calculation Method of Sweep Efficiency after Pattern Infilling in Low Permeability Reservoir

Sweep efficiency is a very important parameters for development effect evaluation and dynamic analysis of oilfield. For low permeability oilfield, well pattern thickening is one of the most effective means of improving development effectiveness. In this paper, a corrected calculation method is given and well spacing density is introduced as a parameter for the formula correction. The curve of volumetric sweep efficiency and well spacing density was achieved through the formula and statistical data. After the infill adjustment, increasing multiple of sweep efficiency can be calculated. Using the actual data of Changqing oilfield to calculate, result show that the deviation is 1.1% .

Distribution of discontinuous mudstone beds within wave-dominated shallow-marine deposits: Star Point Sandstone and Blackhawk Formation, Eastern Utah

Deposits of wave-dominated shorelines are typically considered to act as relatively simple hydrocarbon reservoirs and are commonly modeled as “tanks of sand.” However, important heterogeneities that can act as barriers to fluid flow occur at the parasequence, bedset, and bed scales, especially in viscous oil or low-permeability oil fields. Heterogeneities at the parasequence and bedset scales have been well studied, but discontinuous mudstone beds occurring within the shoreface have received little attention. The Book Cliffs and Wasatch Plateau are among the best-exposed and best-studied deposits of wave-dominated shallow-marine systems in the world. Two parasequences within these outcrops have been studied in detail to investigate the distributions of intrashoreface shales and to propose models for the controls on their distribution. A data set consisting of 30 km (18.6 mi) of virtual outcrops derived from oblique helicopter-mounted light detection and ranging (LIDAR) scanning with supporting stratigraphic sections makes it possible to collect a large quantity of accurate geometric data of depositional elements from inaccessible cliffs. Nine-hundred and twenty-one discontinuous mudstone beds were measured. These occur as ellipses with long axes oriented normal to the paleoshoreline. Lengths and widths of these mudstone beds exhibit a lognormal distribution, with means of 21.9 and 13.8 m (71.9 and 45.3 ft), respectively. Within the shoreface succession, the number of mudstone beds increases downward whereas size does not vary significantly with stratigraphic height. An average of 100 m (328 ft) cumulative length of shale exists per 100 m (328 ft) of horizontal outcrop; this increases threefold near both wave-dominated deltas and bedset boundaries that reflect minor sea-level fluctuations during progradation.

Simulating Multizone Fracturing in Vertical Wells

Numerous multizone multistage hydraulic fracturing treatments are now being executed in low permeability oil and gas fields around the world. Due to the limited access to the subsurface, post-treatment assessments are mainly limited to few techniques such as tiltmeter, microseismic, and tracer-logs. The first two techniques are mainly used to determine fracture extension; however, fracture height and fracture initiation at all perforation clusters could only be confirmed through radioactive tracer logs or detailed pressure analysis. In this paper, we consider real examples from a field from Central America and investigate potential problems that led to the limited generation of fractures in multizone treatments. For instance, some of the postfrac radioactive logs show very low concentration of tracers at some perforated zones in comparison with other zones. On the other hand in some cases, tracer logs indicate the presence of tracers in deeper or shallower zones. Different reasons could cause fracture growth in nonperforated zones, including but not limited to: perforation design problems, casing/cement integrity problems, lack of containment, instability of fracture growth in one or some of the zones, and finally making a mistake in selecting lithology for fracturing. In this paper, some of these issues have been examined for a few sample wells using treatment pressure data, petrophysical logs, and postfrac tracer logs. Some recommendations in designing the length and arrangement of perforations to avoid these problems in future fracturing jobs are provided at the end of this paper.

Parameters Optimization of Fractures with One for Injection and Two Others for Production of Horizontal Wells Fracturing on Offshore Oilfields

This article presents a new exploitation method based on the same fractured horizontal well with fractures for injection or production on offshore low permeability oilfields for the purpose of adapting to their practical situations and characteristics, which means fractures close to the toe of horizontal well used for injecting water and fractures near the heel of horizontal well used for producing oil. According to proposed development mode of fracturing, relevant physical model is established, Then reservoir numerical simulation method has been applied to study the effect of arrangement pattern of injection and production fractures, fracture conductivity, fracture length on oil production. Research indicates cumulative oil production is much higher by employing the middle fracture for injecting water compared with using the remote one, suggesting that the middle fracture adopted for injecting water, and hydraulic fracture length and conductivity have been optimized. The proposed development pattern of a staged fracturing for horizontal wells with some fractures applied for injecting water and others for production based on the same horizontal well provides new thoughts for offshore oilfields exploitation.

Research of Water Quality in Typical Low Permeability Oilfield Produced Water Treatment

It is significative to study sewage treatment process in low permeable oil fields. It could enhance the oil recovery. The water quality characteristics and oil/water separation characteristics were researched during different period process by GC-MS. It shows that there are about 108 kinds of organic matters, including 45 kinds of aliphatic hydrocarbon, 7 kinds of aine, 5 kinds of sulfocompound and 9 kinds of hexacyclic compounds, such as Benzene, phenol, naphthalene and anthracene. The percent of oil droplets which size was less than 10μm is 57.3%, compared to 91.6% which size was more than 50μm. It is difficult to separate the water and oil. The remaining oil was emulsified oil. The process was hard to decrease COD, and some pollutants were existed in water, such as Arsenic, Selenium, Mercury ,Cadmium and Cr6+. It is further proposed to optimize and develop this process to removal oil and suspended solids.

Low Permeability Reservoir Water Displacing Oil and Water Flooding Characteristic Curve Theory

The so-called water flooding characteristic curve refers to the oilfield water injection (or natural water drive) development process, a relationship between curve cumulative oil production, cumulative water production and accumulation of fluid production. These curves have been widely used for water injection development of dynamic and recoverable reserves forecast. After many years of practical application, summed up the four kinds of water drive characteristic curve, they have a good practical significance. Recoverable reserves are important indicators of field development is the main basis for planning and design, the application of waterflooding characteristic curve can be predicted oil recoverable reserves. Four water flooding characteristics discussed above curve is mainly applied in high-permeability oil field, which did not consider starting pressure, but should consider the impact of low permeability oilfield actuating pressure gradient on the moisture content.

State-of-the-Art Hole-Cleaning Techniques in Complex Structure Wells

Complex structure wells are now widely used in the development of marine oilfield, old oilfield and low permeable oilfield. During drilling operations, if the fluid velocity is lower than a critical value in annulus, cuttings in the highly-deviated segments and horizontal segments will accumulate and eventually develop cuttings bed, which affects the rate of penetration (ROP) and downhole safety. As a result, numerous inventions which show different hole-cleaning detection methods can be applied to determine cuttings concentration or hole-cleaning efficiency, and there are three methods for good hole-cleaning condition. The fluid rate control methods include increasing flow rate and injecting slug. The chemical methods include changing the rheology of drilling fluid and adding fiber sweep into drilling fluid. The mechanical methods include using pipe joint, annulus reducer, and different types of blades tool for rotary drilling, and centralizer and fluid velocity shift device for non-rotary drilling and rotary drilling. This review presents a summary of the main United States and Chinese patents available on hole-cleaning techniques.

Analysis of Factors of Affecting Pump Efficiency in Low Permeability Oil Field

Aiming at the characteristics of the production in low permeability oil field, the pump efficiency mathematic model is built. Then the factors of affecting the pump efficiency are analyzed, which include the liquid production, diameter of pump, pump depth, immerse depth of pump, stroke and stroke per time, gas oil ratio, inclined angle of pump and discontinuous production efficiency. Through the theoretical calculation, the main factors of affecting the pump efficiency is determined, which are the liquid production, diameter of pump, stroke per minute, pump depth, inclined angle and discontinuous production efficiency. According to the calculation results, it can supply the theoretical foundation for the oil production.

特低渗碎屑岩储层评价方法研究——以安塞油田三叠系延长组长6油层组为例

中国的地质演化特点决定了中国的低渗透油气资源丰富，分布广、类型多、资源量大。在我国经济快速发展但能源紧缺的情况下，大力加紧低渗透储层的评价研究，解决低渗透油层的勘探开发难题，加快增储上产的步伐，对促进国民经济持续稳定发展具有现实的和科学的意义。我国第一个规模开发的低渗透油田——长庆安塞油田，是一个特低渗透油田。本文以安塞油田三叠系延长组长6油层组为例，从沉积体系研究低渗透油气田的分布规律，通过精细的沉积微相分析，了解低孔低渗砂体纵横向分布状况；通过成岩作用分析，确定储集体的成岩演化序列、成岩相分布；通过储层评价，认清储层的孔隙结构和物性特征，建立低渗储层评价方法和分类标准，优选有利区并完成储层预测。 The characteristics of geological evolution in china determine that low-permeability oil and gas resource is abundant, widespread and has various types. In the rapid economic development of our country with energy shortage situation, intensifying the research and evaluation of low permeability reservoir, solving the problem of exploration and development of low-permeability reservoir, accelerating the increase in oil reserve and production to promote sustained and stable development of national economy have the realistic and scientific significance. Changqing Ansai oil field, the first large-scale development of low-permeability oil field, is a low-permeability oil field. In this paper, we take the Chang 6 reservoir of Yanchang Formation in Ansai district as an example to study low-permeability oil and gas distribution rules by depositional system. We can understand horizontal and vertical distribution of low-permeability reservoirs through refined sedimentary micro-facies analysis. The diagenetic evolution sequence and diagenetic facies distribution in the reservoir can be confirmed by the method of diagenesis analysis. Finally, through reservoir evaluation, we can recognize the reservoir pore structure and physical characteristics, establish the evaluation method of low-permeability reservoir and classification standard, optimize advantageous area and complete the reservoir prediction.

Experiment Research on Enhanced Oil Recovery by Intermittent Gas Injection in Low Permeability Oilfield

Experiment Research on Enhanced Oil Recovery by Intermittent Gas Injection in Low Permeability Oilfield

The Detailed Study for Barrier and Interlayer of Low Permeability Reservoirs in Sha-4 Formation of W81 Block, Dongpu Sag

W81 Block is located in the northern end of central uplift in Dongpu Sag and is a deep part of the Weicheng Oilfield structure. By detailed core observation and analysis of logging data characteristics, we can identify two main types of barrier and interlayer in Sha-4 Formation, including muddy barrier and interlayer and gray interlayer. This article describes the distribution characteristics of the barrier and interlayer from three aspects: plane, crosswell profile and well group distribution. The corresponding three-dimensional distribution model of the barrier and interlayer based on structural model has been constructed, which reflects the distribution rule across the barrier and interlayer and help to guide internal dig potential development of the low permeability oilfield.

Investigation of Well Patterns of Horizontal-Vertical Wells for the Exploitation of Tight Reservoir

In general, the scale of production, exploitation period and the economic benefits of oil and gas field are, to a large extent, depended on the selection, deployment and adjustment of well patterns, especially for tight reservoir. So far, some problems exist in Changqing low permeability oil field, such as the effective displacement system is not easy to be established, a low utilization efficiency of injection water, low oil production and so on. Therefore, five kinds of different well pattern schemes are designed. Then, the well pattern schemes are optimized through numerical simulation method based on the exploitation index including the daily oil output per well, moisture content and oil recovery. Results show that the well patterns of horizontal-vertical wells have better development efficiency than the well patterns of vertical wells. For the optimized well pattern, when the horizontal segment length of horizontal well is 300m, the optimalizing well spacing is 400m and the optimalizing row spacing is 100~150m.

The Numerical Simulation of non-Darcy Flow for YuShulin Low Permeability Oilfield

In this paper, a mathematical model for non-Darcy flow in low permeability oil reservoirs is developed, considering the threshold pressure gradient. The model is then discretized into difference equations and solved. FORTAN99 language is used to program the 3D three-phase numerical model for non-Darcy flow in the simulation software. FORTAN99 is used, because it is fast when performing huge engineering calculations. The pre and post processing system for the simulation software is developed using DELPHI language, because it has good interface with WINDOWS and has ability to manage databases. Numerical simulation is done in the simulation software combined with actual data from Yushulin low permeability oilfield. The effects of threshold pressure gradient, well spacing, and water injection modes are investigated. Results show that as the permeability increases from 1×10 -3 μm 2 to 12×10 -3 μm 2 , the sweep efficiency and the water displacement recovery also increases significantly. When the permeability of reservoir is fixed at 5×10 -3 μm 2 , the threshold pressure gradient increases as the well spacing decreases from 350m to 150m. Compared with the inverted nine spot water injection pattern, the sweep efficiencies for the line water injection pattern and the fivespot water injection pattern increase by 6.64% and 7.78%, respectively. The water displacement recoveries for them are increased by 2.94% and 3.57%, respectively.

Reasons for Formation Damage and Preparation for Disentanglement Agent in Low Permeability Oilfield

For the characteristics of serious formation damage and insufficient injecting in injection wells in the water flooding development process in low permeability oilfield, it carries the analysis of reasons for forming low efficient injection wells and the development of acidizing disentanglement agent. Through core damage experiment of wellhead sewage in S oilfield, formation damage is mainly caused by excessive levels of suspended matters and the multiple of exceeding standards is 45.3. Based on the result of core damage experiment and actual oilfield production data, the variation of apparent injectivity index in low efficient injection wells is researched. The research result indicates that formation damage radius of pollution wells is about 20m in this oilfield. Based on formation damage condition of this oilfield, compound acid is developed, which has the properties of strong penetration, retarding reaction velocity and strong-chelating. Plug removal experiment indicates that the recovery rate of core permeability is about 100% using developed compound acid.

Numerical Simulation Research on Reasonable Production Time Limit Optimization of Advanced Water Injection in Low Permeability Oilfield

Based on the characteristics of low permeability, low pressure, poor effect of conventional waterflood development and low recovery efficiency in Chao Yanggou oilfield, advanced water injection is applied. Taking the Chang 10th block of Chao Yanggou oilfield as an example, the research on reasonable production time and pressure limit of advanced water injection in low permeability oilfield are carried out using methods of numerical simulation and reservoir engineering. The result shows that the average permeability of the Chang 10th block is 7.0×10-3μm2, the reasonable time of advanced water injection is about 6 months, and the recovery efficiency increases 2.26% compared with synchronized water injection. The successful application of advanced water injection development technology has some guidance on low-permeability oilfield development.

The Study of the Start and Stop Cycle of the Gathering and Transportation by Electrical Heating

The gathering and transportation technology on electrical heating is one of major ways of the gathering and transportation for low permeability and low-yielding oil field, this paper has set up the physical model and mathematical model of the gathering and transportation that is controlled by time. By solving the model, we can determine the start and stop cycle of the gathering and transporting pipelines and dendriform net by electrical heating. And we also have conducted field test, the experiment turns out that the error of the result which is calculated by model compared with actual operational result is less than 1%, the phenomenon meets the requirements of production, the results can be used to determine the start and stop cycle of the gathering and transportation by electrical heating in the process of production.

A Combined Solution Model for Predicting Development Performance of Low Permeability Reservoirs

Production prediction model and waterflooding characteristic equation considering threshold pressure were deduced. Based on them, a combined solution model was established, which can predict development indexes in low permeability reservoirs. The development indexes of a typical low permeability block YS2 were forecast using the combined solution model. Forecast results and actual production data fit well, which confirms the practicability and validity of the combined solution model. It has important practical significance to guide low permeability oilfield development.

Review and Analysis of Cuttings Transport in Complex Structural Wells

Complex structural wells are widely used in the development of marine oilfields, old oilfield sand low permeable oilfields. However, poor hole cleaning often occurred in the highly-deviated sections and horizontal sections of the complex structural wells, which affects rate of penetration, cementing quality and downhole safety. It is advisable to study the behavior of cuttings transport under different conditions. In general, experimental observations and CFD simulations are main methods to analyze the effects of cutting parameters, fluid parameters and operational parameters on hole cleaning. The correlations and models are applied to predict the number of cuttings and the critical velocity in the annulus. In this paper, an analysis of key parameters is conducted on cuttings transport, the existing problems and characteristics of these correlations and models are summarized,, and different removal methods of annular cuttings and future research needs are discussed. Although major improvements have been achieved in the past several decades, how to accurately predict the cuttings bed height, critical velocity and other key parameters, and to effectively solve the poor hole cleaning still is a difficulty challenge. Therefore, more research will be conducted to further understand cuttings transport mechanism in multi-factors coupling and complex wellbore conditions.

Numerical Simulation of Deflection Fracturing with Finite Element Method Considering Crack Initiation Angle

Aimed at deflection fracturing by oriented perforation, a two-dimensional, non-steady and two-phase Finite Element Method (FEM) is established. Taking a battery of wells in the inverted nine-spot rhombus pattern as object of study, it is reported that law of different crack initiation angle (CIA) affecting deflection fracturing. In the respect of daily oil production and cumulative oil production, the dual fracture with different CIA is more than straight fracture. So it is feasible to use deflection fracturing of oriented perforation to increase the production of the special low permeability oilfield. In contrast to dual fractures with different fracturing initiation angles, we can see that the wider CIA, the higher cumulative oil production. So we can draw such a conclusion that when deflection fracturing is implemented, angle should be increased if the working condition is permitted so as to increase the production of oil well.

Field Test of Carbon Dioxide Gas Channeling Foam Plugging

Gas channeling is tending to happen in CO2 immiscible flooding process, and that would seriously influence gas injection development. In order to plugging gas channeling channel effectively, improve inspiration and production profile, and enhance swept volume and oil displacement efficiency of the gas injection, field trials of foam seal channeling are carried out. The tests showed that carbon dioxide foam can effectively plugging the gas channeling channel, expand the swept volume of carbon dioxide gas, reduce invalid circulation, and enhancing oil displacement efficiency. The anti-sealing channeling technology is cost-efficient, and it is suitable for Daqing peripheral low permeability oil field on gas injection development. It has good prospects, and it will provide a strong technical support on gas injection development of low permeability reservoir.