Thick Oil Reservoir Research Articles

Physical modeling of development adjustment mechanism for heterogeneous thick oil reservoir

With the gradually deep development of oil field, the remaining oil in reservoir become more scattered, to exploit them within the high water-cut pay become extremely difficult. Based on the characteristics of extremely high water-cut reservoir, three large scale physical models with different injection-production well patterns are designed. Through the analysis of oil production rate and the data of Computed Tomography (CT) scanning, the change law of fluid content within the core are obtained; The new calculation method of sweep efficiency for waterflooding within non-homogeneous models are set up in accordance with the CT number at different waterflooding stages. Furthermore, the development results of different plans are compared with each other, both injection and production with horizontal wells at low-permeability formation have the best recovery, because the displacement fluid can reach the places in reservoir where conventional waterflooding cannot. Therefore, this well pattern is the optimum plan for the positive rhythm model in this experiment, and the development strategy optimization is realized for high water-cut thick oil formation.

Experimental Study on Vertical Propagation Behavior of Hydraulic Fracture Affected by Artificial Interlayer for Thick Oil Reservoirs

Crude oil distribution in thick oil reservoirs is vertically heterogeneous; therefore, there is usually a dominant sublayer where oil resources are higher than that in other sublayers. The region of hydraulic fracture away from the dominant sublayer plays a negative role in production. In order to enhance efficiency of hydraulic fracturing, the hydraulic fracture height should be restricted around the dominant sublayer and the artificial interlayer is believed as an effective method. However, the propagation mechanism of fracture affected by artificial interlayer has been rarely investigated, which restricts the advance of optimization of artificial interlayer. In this paper, the impact of artificial interlayer on vertical propagation of hydraulic fracture is analyzed by hydraulic fracturing experiments and then the mechanism of artificial interlayer affecting propagation of hydraulic fracture is discussed. Based on the understanding of experimental observations and theory of fracture mechanics, the theoretical model of stress intensity factor for the fracture affected by artificial interlayer is proposed. The experimental data shows that the artificial interlayer can significantly decrease the hydraulic fracture height and the corresponding decrease magnitude of hydraulic fracture height depends on the thickness of artificial interlayer, proppant size, and fracture fluid pumping rate. The dominant mechanism of artificial interlayer restricting hydraulic fracture height is that the drop of fluid pressure induced by the artificial interlayer decreases the stress intensity factor at fracture tip. Based on the theory of fracture mechanics, the stress intensity factor at fracture tip is built and it can consider key factors shown by experimental observations. The fracture height solution from this model is consistent with experimental data, so this model can be used to optimize properties of artificial interlayer.

Research on well selection and layer selection methods for tapping the remaining oil at the top of thick oil layers using ultra-short radius lateral drilling horizontal wells

The flexible drilling method of ultra-short radius sidetrack horizontal wells is an effective method to utilize the remaining oil at the top of thick oil reservoirs. By analyzing the current status of the SZ oilfield well network, development stage and sand body development characteristics, combined with the characteristics of ultra-short radius lateral drilling horizontal well technology, the areas and formations suitable for ultra-short radius lateral drilling horizontal well tapping are identified, and the criteria for selecting wells and formations for ultra-short radius lateral drilling horizontal wells are established, which is a guide for the application of this technology.

Experimental Study on Sweep Characteristics of Gas Gravity Drainage in the Interlayer Oil Reservoir

Stable gas gravity drainage is considered an effective method to enhance oil recovery, especially suitable for deep buried, large dip angle, and thick oil reservoirs. The influence of reservoir heterogeneity on controlling the gas–oil interface and sweep characteristics of injected gas is particularly important to design reservoir development schemes. In this study, according to the interlayer characteristics of Donghe carboniferous oil reservoirs in the Tarim Basin, NW China, 2D visual physical models are established, in which the matrix permeability is 68.1 mD and average pore throat radius is 60 nm. Then, hydrocarbon gas gravity drainage simulation experiments are carried out systematically, and a high-speed camera is used to record the process of gas–oil flow and interface movement. In this experiment, the miscible zone of crude oil and hydrocarbon gas is observed for the first time. The interlayer has an obvious shielding influence, which can destroy the stability of the gas–oil interface and miscible zone, change the movement direction of the gas–oil interface, and reduce the final oil recovery after gravity drainage. The remaining oil mainly is distributed near the interlayers. The higher displacement pressure leads to increased stability of the gas–oil displacement front and later gas breakthrough, which leads to higher oil recovery. The lower gas injection rate contributes to a slower front velocity and wider miscible zone, which could delay gas breakthrough. For the immiscible gas gravity drainage, there is a critical gas injection rate, with which the oil recovery factor is the highest.

English

At present, the effect of different development patterns of interlayer like the length and the longitudinal position of interlayer on thermal recovery modes such as steam stimulation (CSS) and steam flooding (SF) is still a qualitative understanding, and there is no systematic study yet. Therefore, it is difficult to control the thermal production of thick oil reservoirs according to different interlayer patterns. In order to quantitatively analyze the influence of interlayer distribution pattern on steam huff and puff and steam flooding of horizontal wells in thick heavy oil reservoir, a numerical simulation model was established based on typical parameters of LD21 heavy oil reservoir in Bohai in China. Through comparison and research on the different modes of development longitudinal position, development length and development scale in non-permeable interlayer and semi-permeable interlayer. The influence of interlayer on the expansion law of steam chamber and ultimate oil recovery degree during steam huff and puff and steam flooding, and the main controlling factors of interlayer influencing oil recovery were obtained. The research results can be used for reference to optimize the location of thermal wells in thick heavy oil reservoir and reduce the influence of interlayer on thermal production effect of horizontal wells. Key words: Heavy oil reservoir; interlayer; steam huff and puff; steam flooding; recovery. &nbsp

3D Experimental Investigation on Enhanced Oil Recovery by Flue Gas Coupled with Steam in Thick Oil Reservoirs

Flue gas is a kind of non-condensate gas that mainly consisted of CO2 (volume percentage about 20%) and N2 (volume percentage about 80%), and is applied in petroleum industry as a kind of displacement agents. In this paper, flue gas is introduced into the thermal recovery process of thick heavy oil reservoir. First, the dissolution characteristics of flue gas in crude oil were researched through the PVT experiments under different conditions. Then, a series of 3D physical simulations were carried out to analyze the oil displacement effect of flue gas coupled with steam flooding in thick reservoir with the consideration of the important production parameters including oil production, water cut, oil-steam ratio and oil recovery in both steam flooding process and the flue gas coupled with steam flooding process. Finally, the EOR mechanisms of flue gas coupled with steam flooding were summarized by analyzing the variation of temperature field, the properties of heavy oil and the distribution of remaining oil....

Numerical study of the water channeling problem in fractured thick oil reservoir

For the fractured thick oil reservoir of LiaoHe oilfield, water channeling controlling is the key issue of the enhanced oil recorvery in next stage. A high-speed numerical method is proposed in this work and is used in the study of the cause of water channeling and how to control water channeling. Water saturation is updated by calculating the pressure balance of adjacent grid so that pressure solving in each step is not needed. The method is more concise than streamline method for the non-necessity of streamline calculation. Moreover, it is 30 times faster than the traditional IMPES method with comparable precision. Specific to the complex geologic body and horizontal well network, by the investigation of the controlling factors of water channeling, two dimensionless number, Ⅱ g and Ⅱ ex are defined to represent the ratio of gravity-driven flow vs. production flow and the ratio of fracture-matrix exchange flow vs. production flow. The influences of Ⅱ g and Ⅱ ex on water channeling are studied numerically. A zone chart of the strength of water channeling, which depends on Ⅱ g and Ⅱ ex , is obtained. The variation tendency of water channeling with Ⅱ g and Ⅱ ex is analyzed. The result of the research has guiding significance for enhanced oil recorvery of LiaoHe oilfield.

Determination of Residual Oil Distribution after Water Flooding and Polymer Flooding

In this study, we want to seek for the results from a study on a reservoir with a single sand body and vertical segmentation to simulate each sand layer individually by using FCM and Petrel software. The results indicated that the black oil simulator E100, the Cartesian coordinate system, the angular point grid and the full implicit solution were used in historical fitting. And plane by 50 for step, the plane was divided into six grids and was vertically divided into six simulation layers. After grid coarsening, the total is 181170. For the oil reservoir block, the fitting error of the cumulative oil production history is 8.65% and the fitting error of the moisture content is 3.42%. For single-well oil production, the mean error is 7.36%, and the mean fitting error of the moisture content is 4.37%. The residual oil remained on top of the thick oil reservoir channel sand after water flooding and is 50.63% of the total surplus geological reserves. Thus, water flooding can improve oil recovery in highly permeable zones. After polymer flooding in a thick reservoir with a top layer of channel sand, the residual oil was 39.26%, which is 11.37% lower than that after water flooding.

Research of Guantao Thick Oil Reservoir Contrast Model in Gudao Oilfield

Southwest Gudao oilfield of heavy oil reservoir characteristics is complex, the fine reservoir division and correlation for increase in oil reserve and production is of great significance. According to the reservoir multi-level contrast method, will study area Ng5-6 sandstone group is divided into 11 small layer, 14 deposit time unit, and to establish a comparison model of reservoir. Reservoir contrast results and its application effect is good, improve the research area of thick oil development effect, and the economic benefit is remarkable.

Geological and geochemical studies of heavy oil reservoirs in China

Thickened heavy oils in China are genetically characteristic of continental fades. As to their physico-chemical properties, these oils are very high in viscosity and low in sulphur and trace element contents. In the group constituents, the concentrations of non-hydrocarbons and asphaltene are very high but those of saturated hydrocarbons and aromatics are very low. The gas chromatograms of alkanes show that these heavy oils have high abundances of iso - alkanes and cyclic hydrocarbons. In all the steroids and terpenoids, bicyclic sesquiterpenoids, tricyclic diterpenoids, re - arranged steranes and gammacerane are strongly biodegradation - resistent. The formation of heavy oil reservoirs is controlled mainly by late basin ascendance, biodegradation, flushing by meteoric water and oxidation in the oil - bearing formations. According to their formation mechanisms, heavy oil reservoirs can be classified as four categories: weathering and denudation, marginal oxidation, secondary migration and thickening of bottom water. Spatially, heavy thick oil reservoirs are distributed regularly: they usually show some paragenetic relationships with normal oil reservoirs. Heavy oil reservoirs often occur in structural highs or in overlying younger strata. Their burial depth is about 2000m. Horizontally, most of them are distributed on the margins of basins or depressions.

Numerical Coning Applications

Abstract An analysis of water or gas coning behaviour is particularly important in determining the future performance of gas reservoirs and thick oil reservoirs of the Rainbow-Zama- Virgo types. Investigations of coning in these reservoirs have only recently become practical. This paper describes results from two numerical coning studies - one a gas-water problem, the other a three-phase problem in a Virgo reef. The implicit numerical model used is described in detail. INTRODUCTION THE CONTROL OF GAS AND WATER CONING in petroleum reservoirs is essential in optimizing recovery and minimizing operational costs. Coning is the result of high-pressure gradients around the producing well which cause the oil-water contact to rise and the gasoil contact to depress near the wellbore. Gravitational forces tend to segregate the fluids according to their densities. However, when gravitational forces are exceeded by the flowing pressure, a cone of water and/ or gas will penetrate the producing interval. Only recently has it become practical to investigate coning as a non-steady-state flow phenomenon with heterogeneous reservoir properties. These investigations are now practical utilizing numerical coning models. Coning is simulated with a 2D radial (R – Z) grid system extending out from the wellbore to some external radius (Re). To obtain proper definition of the gas and water cones, a fine grid is used near the wellbore. The pore volumes of these interior grid blocks are typically 1 to 10 barrels, At a normal producing rate and with a reasonable time-step size, the fluid throughput per time step of the inner blocks is many times the pore volume of the blocks. This high throughput causes large saturation changes per time step and, in the past, these large saturation changes have caused model instabilities. Normally, in a reservoir simulator the transmissibilities governing flow between blocks and the production rates of oil, gas and water are calculated explicitly using the saturation conditions existing at the beginning of the time step. If explicit transmissibilities and production terms are used in a coning model, a practical time-step size will cause the predicted saturations to become unstable and the GOR's and WOR's to oscillate, These instabilities can be controlled by treating the transmissibilities and production terms implicitly rather than excplicity. The computation required per time step increases with a totally implicit model, but the resulting increase in the time-step size which can be taken more than offsets the greater computation requirements. The net result is a numerical model which can be used routinely, at low cost, on practical problems. The Appendix describes in detail the mathematics of this coning model. The following section describes two coning studies. The first case is a gas pool with an underlying aquifer. The second is a single-well bioherm reef being produced under primary depletion. Initially, it is without a gas cap, but it does have a small underlying aq Uifer, Both studies used a fully compressible threephase 2D radial model.