Edge Water Reservoir Research Articles

Vector well pattern optimization of horizontal well in offshore edge water reservoirs

The L30up reservoir is a strongly heterogeneous edge water reservoir with obvious provenance direction and channel direction. It is developed by horizontal wells, and the traditional well pattern adjustment is not suitable for tapping the remaining oil potential of this type of reservoirs, while vector well pattern adjustment is one of the important measures to enhance oil recovery. In this paper, aiming at maximizing the economic net present value, taking the characteristic parameter matrix of well pattern reconfiguration (well position, azimuth angle, horizontal section length) as variables, an optimization model of horizontal well pattern vector adjustment is established. Furthermore, the PSO-MADS algorithm is proposed to solve the above optimization model. Thus, a vector well pattern adjustment technology that can realize the distribution matching of reservoir heterogeneity and remaining oil has been formed. On the basis of the deployment strategy of vector well pattern in L30up reservoir, according to the direction of sediment source, reservoir heterogeneity, distribution of remaining oil, etc., we determined the best vector well pattern adjustment scheme, and applied the above optimization method to optimize the infill well locations. Through the optimal deployment of the vector well pattern, the oil recovery factor after the vector well pattern adjustment is 5.21% percentage points higher than the original well pattern conditions, which precisely matches the well pattern parameters and the geological vector parameters, such as sand body distribution, remaining oil distribution, and edge waters in L30up reservoir.

New Model of Granite Buried-Hill Reservoir in PL Oilfield, Bohai Sea, China

The geological estimated hydrocarbon reserves of the Mesozoic granite buried-hill reservoir in the PL oilfield exceed 200 million tons. During the exploration stage, it was commonly considered that the PL buried-hill reservoir should demonstrate a “layered” edge water reservoir mode, because of weathering and tectonics. However, during a later stage, the formation of water was found at structurally high locations, which does not fit the intuition. Therefore, a suitable model is still lacking. Based on the comprehensive information of thin-section, core plug, well logging, and seismic data, etc., the buried-hill of the PL oilfield was re-divided into three northeast–southwest-trending zones. In this model, the reservoir is layered, with each layer having the characteristics of bottom water and two kinds of horizontal and vertical seepage. This new model fits the field-drilling test very well. These insights can effectively guide the exploration and development practice for this kind of buried-hill.

Study on migration characteristics of oil gas water three-phase interface and distribution law of remaining oil in gas cap edge water reservoir

ABSTRACT Reservoirs with gas cap and edge water grow rapidly in the early stage of development, the oil well has no water, the recovery period is short, the three phases of oil, gas, and water are easy to cross each other, the production decreases rapidly, and the development is difficult. Therefore, it is necessary to clarify the migration law of oil, gas, and water three-phase interface, find out the distribution law of remaining oil, and put forward the direction of EOR. In order to study the migration law of oil, gas, and water three-phase interface in the development of this kind of reservoir, taking JZ25-1S gas cap edge water reservoir as an example, a three-dimensional physical model is established based on the similarity criterion. The characteristics of fluid interface migration and the distribution of remaining oil under depletion development and barrier waterflood development are studied through experiments. The research results show that gas channeling occurs after 30 minutes of depletion development, and the migration speed of the oil-gas interface is faster than that of the oil-water interface, and the migration speed of the high-permeability layer is faster. The remaining oil in the low-permeability layer is mainly distributed on both sides of the oil and gas and oil-water channels, and the remaining oil in the high-permeability layer is mainly composed of rock particles, pore walls, and surfaces of interstitial materials. The ultimate recovery rate of depletion development is 25%. At the barrier waterflooding development for 60 minutes, gas began to appear, the migration rate of oil-gas and oil-water interface was stable, and the shape of fluid interface was gentle. A small amount of remaining oil in each permeability layer is distributed in the oil ring and gas cap area, and the distribution of remaining oil is mainly affected by injection timing and injection-production ratio. The final recovery rate of barrier waterflooding development is 51%, which is 26% higher than that of depletion development. The findings of this study can help for better understanding of great significance to the formulation of production parameters for depleted development of gas cap and edge water reservoirs and the implementation of later production stimulation measures.

Study on Screening Criteria of Gel-Assisted Polymer and Surfactant Binary Combination Flooding after Water Flooding in Strong Edge Water Reservoirs: A Case of Jidong Oilfield.

Strong edge water reservoirs have sufficient natural energy. After long-term natural water flooding development, it is in the stage of ultrahigh water cut. There is an urgent need to change the development mode and improve the development effect. Taking Jidong Oilfield as an example, the mechanism model of strong edge water reservoirs is established by using the method of numerical simulation. Then, the factors and rules affecting the effects of gel-assisted polymer and surfactant binary combination flooding are studied. The screening criteria of gel-assisted polymer and surfactant binary combination flooding in strong edge water reservoirs are obtained. The results show that the existence of edge water is not conducive to binary combination flooding. Smaller water volumetric multiples and larger oil-bearing areas are more suitable for binary combination flooding. Compared with closed reservoirs, binary combination flooding in strong edge water reservoirs is more difficult to establish a displacement pressure gradient. The reservoir with high crude oil viscosity is not suitable for binary combination flooding. Gel-assisted polymer and surfactant binary combination flooding can be adopted for reservoirs with an oil-bearing area greater than 0.2 km2, a water volumetric multiple less than 200, and oil viscosity less than 100 mPa·s. The research results are of guiding significance for the reservoir selection of gel-assisted polymer and surfactant binary combination flooding after natural water flooding.

A water invasion unit numerical simulation model for the distribution of water and water invasion channel in complex edge water reservoir

In order to accurately and intuitively characterize the distribution of water and water invasion channel in complex edge water reservoir, a water invasion unit numerical simulation model (WINS) that can simulate complex edge water invasion dynamics is established, based on well geological data and production data. The model discretizes the edge water into water unit connected to the production well unit, and discretizes the locations with clear geological understanding into dense unit. The more dense units, the more accurate the water invasion dynamics. Based on the water unit, production well unit, dense unit, the material balance method is used to calculate the pressure of each unit, the water flooding front propulsion equation is used to calculate the saturation and water cut of each unit, and the genetic algorithm is combined to modify characteristic parameters of the water unit and the water invasion channel, fit automatically production data, realize the re-identification of water distribution and water invasion channel. Different edge water and high-permeability bands are constructed through numerical simulator, and the simulated production results are substituted into the model to automatically fit. The results show that the edge water distribution and water invasion dominant channel inversely performed by WINS are consistent with the results constructed by the numerical simulator. Compared with the process of constructing edge water at the reservoir by Eclipse numerical simulator, WINS saves the tedious steps of building a model, and its calculation efficiency is higher. Not only that, WINS can intelligently and automatically fit parameters, reducing errors caused by human interference.

3D Physical Simulation Experiment of Edge Water Reservoir by Polymer/Surfactant Binary Flooding

To investigate the enhanced oil recovery (EOR) technology by chemical flooding in an edge water reservoir, a 3D physical simulation experimental device for the edge water reservoir was developed, and polymer/surfactant binary flooding experiments were carried out under different edge water energies. In addition, the effect and mechanism of binary flooding on EOR under different edge water energies were comprehensively analyzed. Experimental results show that edge water intrusion considerably affects EOR by binary flooding. The stronger the edge water energy, the worse the effect of EOR by binary flooding. Edge water possibly diluted the concentration of the chemical agent medium that is injected into the reservoir, and the degree of dilution varied in different regions. The dilution region was mainly distributed between the injection wells and edge water. The stronger the edge water energy, the higher the dilution multiple of chemical agent and the greater the recovery loss rate by binary flooding.

Technique policy for concurrent development of natural and artificial water flooding of strong edge water reservoir: A case study of central layer Yu-III of Akshabulak oilfield

The central layer Yu-III in Akshabulak oilfield is a sandstone reservoir with strong edge water, whose major development characteristics are high oil recovery rate and heterogeneous water invasion. Aiming at this problem, the development policy chart of concurrent displacement of natural water and injected water is established on the basis of material balance principle. Injection-production ratio and oil recovery rate are the main controlling factors for the concurrent displacement of natural water and injected water. Each injection-production ratio corresponds with only one rational oil recovery rate, and the rational oil recovery rate increases with the injection-production ratio. When the actual injection-production ratio of the central Yu-III reservoir is 0.9, the rational oil recovery rate should be 4%.

测录井资料在层状边水稠油油藏水淹层识别中的应用

测录井资料在层状边水稠油油藏水淹层识别中的应用

Numerical Simulation Study for Water Breakthrough Law of Horizontal Well in Edge Water Reservoir

There are abundant research achievements for water breakthrough law of horizontal well in bottom water reservoir, but fewer in edge water at home and abroad. BZ Oilfield of Bohai Bay has characteristics of active edge water, well pattern of directional and horizontal wells. At present, there is a lack of understanding of water breakthrough law of horizontal well in edge water reservoir. The paper established a method considering permeability heterogeneity for identifying water breakthrough position of horizontal well in edge water reservoir by using numerical simulation. It has proved that this method is feasible and reliable in BZ Oilfield. Combined with WI decision in breakthrough, put forward some measures for stabilizing oil production and water control, guided the implementation of oilfield measures and stable production.

The Development and Technology Policy for a Gas Cap and Edge Water Reservoir with Narrow Oil Ring

Reservoir with gas cap, edge water is complex. And the oil-water and oil-gas interface will seriously influence the performance. Once out of control, gas and water invasion may occur, then oil productivity will fall sharply and oil recovery will become low. In addition, the oil penetrating into gas cap would lead to oil loss. So, the controlling methods are crucial. In this paper, we study the productive characteristics of a certain reservoir with gas cap, edge water and narrow oil ring. For the phenomenon several productive wells appeared gas breakthrough and water invasion after putting into production, this paper puts up a strategy shutting in high gas-oil ratio wells and blocking off gas breakthrough layers that proved effective. At the same time, adjusting oil and gas distribution underground by gas-water alternate also be proved practicable.

Feasibility Study on Using Nitrogen Foam to Control Water Invasion in Edge Water Reservoirs

We have experimentally studied the effect of the concentration of the foaming agent solution, the permeability, the gas-liquid ratio, and the oil saturation on the performance of a nitrogen foam in plugging edge water. We used a numerical simulation of an edge water reservoir to study the effectiveness of water invasion control by injecting foam into one horizontal or three vertical wells. As shown by the simulation results, injection of foam into a horizontal well can significantly improve oil recovery and reduce water cut, while injection of foam into vertical wells is ineffective. Three factors were optimized that have a significant effect on field development. Adding a high-permeability band to the model demonstrated the applicability of the proposed field development method to heterogeneous reservoirs.

The formation evaluation tool and its application in offshore China

The Formation Evaluation Tool (FET) introduced in the paper represents a new generation of formation evaluation systems developed and manufactured by China Oilfield Services Limited (COSL), CNOOC, using a FET technology transfer from Crocker Research, Australia. The system has been applied successfully in the Bohai Sea and South China Sea. For instance, a multilayered oil and water system has been confirmed with the aid of accurate formation pressure tests, even in very thin beds and edge water reservoirs, overcoming the difficulty of determining this kind of oil-water and gas-water contacts. Moreover, the FET pumping and real-time fluid monitoring function allows acquiring a true sample of formation fluid unpolluted by drilling mud which plays an important role in determining the fluid properties of the target stratum and analyzing the fluid component. The principles and purpose of the Formation Evaluation Tool (FET) will be briefly introduced and successful examples of the application of the technology will be described in detail in this paper.