The production stabilization and water-cut control technology system that could be matched with the development policy is established by technological breakthrough and on-site application according to the profile control, profile displacement, water plugging, plugging removal and other major technical demands for offshore oilfield, with the formation of multiple economic and applicable competitive technological products - microsphere profile displacement, situ gas production displacement, foaming profile displacement, chemical profile control, water plugging, HGSC composite plugging removal, etc.

The production stabilization and water-cut control business covers major oilfields in Bohai Sea, the Eastern South China Sea and the Western South China sea, and is expanded to Indonesia, Iraq and other overseas markets, and could solve the problems of stabilization yields and stimulation at all stages of oilfield development effectively for customers.

Process Introduction

The microsphere is a dispersed particle gel composited by inverse micro-emulsions polymerization, with average size of hundred of nanometer, which is featured with even dispersion in the water and easy to inject into the formation, and then plays its role in blockage after swelling by absorbing water gradually. The product is characterized by "easy-to-inject, capable-to-block and movable" and other features for deep profile control and displacement

The mechanism of microsphere deep profile control and displacement technology is to block the pore throat of high-permeable bands by swelled microspheres, and then block level by level and change the direction of the water-driven fluid by constant deformation and migration, enlarge its sweep efficiency so as to attain the target of improving the recovery efficiency by deep profile control and displacement.

Technical Indicators

By now, there are three categories, with a total of more than 30 kinds of microspheres that have been developed, and their major technical indicators are shown as follows:

Types	Model	Process Requirements	Formation Adaptation	Initial Size	Full Swelling Time	Final Swelling Size
Final Swelling Size	NM-2	Deep profile control and displacement	＜2000mD	10～200nm	7~30d (adjustable)	Several microns
Composite sphere	FH-260	Deep profile control and displacement	2000～5000mD	300～1000nm	7~20d (adjustable)	Several microns ~ more than 10 microns
Core-shell sphere	HK-4100	Core-shell sphere	2000～5000mD	300～1500nm	7~20d (adjustable)	Dozens of microns

Technical Applicability

Indicator	Microspheres adaptable conditions
Reservoir distribution	Solve the situ and plane contradictions, and enlarge the swept volume of water flooding;
Moisture content	Average moisture content of well group: 50%~95%
Connectivity	The target layers have better connectivity, with the injection-production connection rate of 65%;
Pore throat distribution	Diameter of reservoir pore passage<50 μm;
Temperature	Reservoir temperature ≤ 130℃;
Mineralization	＜200000ppm

Supporting Systems, Software and Tools

Microspheres product design and evaluation techniques, microsphere-formation matching and decision-making method, optimization and design technology for microsphere profile control and displacement parameters, numerical stimulation technology for microsphere profile control and displacement, microsphere detection technology for output liquid, etc.

Methods of Application

Connect with the water injection pipeline for injection, without mixing and curing devices needed, and feature with small floor area required, less equipment used and easy to operate.

Application

At present, the microspheres profile control and displacement technology has been applied on 16 well groups cumulatively in Bohai Bay area, with the average yield increased by 7,761t for each single well group, the average yield increased by 83t per ton of agent, the input-output ratio of more than 1:5.

Case Study

Results on Microsphere Profile Control and Displacement Operation of a Well Group in Bohai Oilfield:

The water content of the well group decreases from 72% to 64%, and its daily oil yield increases from 240 tons/day to 320 ton/day; It was valid for more than 1 year, with accumulative yield increased by 21,000t within such period, and the yield was increased by 138t per ton of agents, with the input-output ratio of 1:7.5, which showed significant economic benefits.

Process Introduction

The situ gas generation technology is designated to generate the gas within and act on the oil reservoir with the injected agent to remove the plug, control the profile and displace the reservoir oil by injecting blowing agent and gas releasing agent into the target formation. It could remove the plug and pollution at the immediate vicinity of wellbore, enlarge the swept volume of the injected water, reduce the oil-water interfacial tension and improve the water-oil mobility ratio by adjusting the dosage of the agents.

Technical Indicators

Valid content of blowing agent >98%, without agglomeration;

Valid content of dispersing agent >98%, without foreign matters;

Valid content of gas releasing agent >31%, without foreign matters.

Technical Applicability

Indicator	Adaptable conditions for situ gas generating technology
Reservoir distribution	The corresponding relation of oil-water well is clear, with strong vertical heterogeneity.
Formation pressure	≥Pb（saturation pressure）
Formation temperature	≥40℃
Remaining oil saturation	≥40%
Viscosity of crude oil	≤300mPa·s
Combined water cut	40%~90%

Supporting Systems, Software and Tools

The reservoir engineering method is used to establish the decision-making method for profile control and displacement of situ gas generation and well selection (layer selection), and build the prediction model and evaluation method for its results, prepare the decision-making software for profile control and displacement of situ gas generation, so as to select the stimulation well preferentially and optimize the parameters of construction technology.

Methods of Application

Connect with construction flow and test the pressure; prepare the agent; inject the blowing agent and gas releasing solution alternatively; take turns to inject the remaining slug; inject the replaced water and restore the water injection after soaking.

Application

As of now, such technology has been applied for 83 well-times cumulatively in the Bohai Sea area, with the cumulative yield increased by 208,000t.

Case Study

The water injection profile of a well in an oilfield in the Bohai Sea is not even, and a total of 4 wells nearby are influenced therefrom.
This well takes the situ gas generating measures, after which the apparent water injectivity index is increased to 45.3 m^3>/(MPa•d) from 37.4m³/(MPa•d), with an increase of the surrounding oil wells in produced fluid and oil production and a decrease in moisture contents, so its efficiency is significant.

Process Introduction

The foaming profile control and displacement (profile) technology is a technique to improve the recovery rate of oilfields by injecting foam fluid into the formation. After injection of the foam fluid into the formation, it could improve the mobility ratio effectively, adjust the injection profile and enlarge the swept volume. The foam is characterized by deforming when meeting with oil and stabilizing when encountering water, so it could block the layer/section with high water contents selectively; the foaming agent is a surfacant component, with the role of improving the displacement efficiency of water flooding.

Technical Indicators

Foaming volume ≥450mL;

Half-life period ≥198min;

Temperature resistance: 120℃；

The resistance effect is improved by more than 5 times as compared with single foaming system.

Technical Applicability

Indicator	Adaptable conditions for situ gas generating technology
Reservoir characteristics	Water flooding reservoir, high water-cut well caused by high interlayer/in-layer/plane heterogeneity
Formation temperature	＜83℃
Viscosity of crude oil	≤300mPa·s
Remaining oil saturation	Relatively high, large potentials
Mineralization	＜2000ppm
Combined water cut	≥80%

Methods of Application

Complete the fluid preparation on the ground, pump by plunger pump, mix with nitrogen on the ground, shaft or within the formation, form the foaming system and then inject into the formation. Using with other technologies like positioning and channeling sealing-off system to enhance its efficiency is another option.

Application

Up to now, the nitrogen foam profile control and displacement technology has been applied in the Bohai Sea area for 4 well-times, with the cumulative increase in yield of over 50,000 tons of oil, achieving obvious oil increase and water decrease.

Case Study

After a well group is conducted with subdivisional injection with nitrogen foam, the fluid production capacity of multiple affected wells increase, and the water cut decreases significantly, with cumulative yield increased by 40,000t within the period of validity. The construction validity is more than 200 days.

Process Introduction

The chemical profile control process is to reduce the permeability of the high-permeability layer/section, reduce the permeability differences between layers by injecting gel that could flow in the large pore path of the formation or fractures into the water injection well, thus attaining the targets of controlling the channeling of injected water, adjusting the interlayer water absorption so as to enlarge the swept volume of the injected water and improve the production of the wells. This technology is mainly dominated by organic gel systems, together with the inorganic gel system, which can be adjusted according to different reservoir conditions, and has been widely used in water-cut controlling and production stabilization measures on offshore oilfields due to its simple process, low costs and safe system, etc.

Technical Indicators

Technical specifications for polymer delayed crosslinking profile control system:

Gelling time: 12~120hrs under 60℃, adjustable;

Gelling strength: Flowable weak gel to non-liquid strong gel; strength after gelling: 60,000~100,000m Pa•s;

Salt-tolerance performance: mineralization of 30,000~50,000ppm;

The gelling strength could be maintained stably for more than 6 months.

Technical specifications for multi-function composite gel profile control agent:：

The resistance to temperature can reach 140℃;

With better salt-tolerance performance, the gelation reaction is free from the influence of hypersalinity and multivalent cations;

The gelling strength could be maintained stably for more than 12 months;

The mobility is better before gelling, achieving the deep profile control;

With better adhesiveness after gelling, and powerful capacity of resistance to flushing.

Technical Applicability

Indicator	Technology for polymer delayed crosslinking profile control system	Technology for multi-function composite gel profile control agent
Development features	The well group is characterized by obvious channeling.	The injected water is featured with clear directional channeling.
Formation temperature	＜90℃	40℃~120℃
Permeability	500~6000mD	2000~200000mD, fracture aperture<2mm
Mineralization	＜30000ppm	＜200000ppm

Methods of Application

Complete the fluid preparation on the ground, and pump into the formation by plunger pump via filter after curing. Subsequently, replace with injected water, test the pressure drop curves, shut-in the well for coagulation, and restore the injection.

Application

The profile control measures have been applied for 30 well-times cumulatively in recent two years, with average increased yield of about 3,000t by such measures, a decrease in average water content of each well group of 3~5%, input-output ratio of more than 1:3.

Case Study

A well in Bohai oilfield:

Problems: 1. The leading edge of the injection well has been advanced into the oil well, with water channeling in large pore path and obvious increase in water contents; 2. With strong interlayer and plane heterogeneity.

Measure effectiveness: an average daily yield increased by 15 tons/day within the validity of measures, a decrease in moisture content of 9%, pure increased production of 2,432t, and production increase in a decreasing manner of 3,156t.

Process Introduction

The Marketing Department has two technologies - chemical commingled plugging and staged packer plugging of horizontal well. For the oil wells with unknown effluent or with effluent from multiple points, the chemical commingled plugging utilizes the plugging agents to plug and seal off the channeling selectively in an automatic control manner, adjusts the producing profile of the oil wells, which is characterized by simple process, low costs and safe systems, etc. The staged packer plugging technology of horizontal wells, determines the water production interval (point) accurately through fiber-optical well logging, array-type multiphase combination logging and other water exploration technologies, attain the targets of locating the water shutoff or chemically plugging the water points, which is featured with high successful rate, large plugging strength, long period of validity, etc.

Technical Indicators

For different reservoir characteristics, the gel series plugging agent, two-phase composite plugging agent, HSG hydrogel and other plugging systems are developed. As different formations have different formulas of plugging agents, the major technical indicators are shown as follows:

 Temperature resistance: 50~130℃;

 Breakthrough pressure gradient: 5~11.67MPa/m;

 Experimental plugging rate: 95~99.8%;

 Oil-water selection performance of plugging agent: Water shutoff ratio/Oil plugging rate >5.

Technical Applicability

Indicator	Technical Applicability
Development features	High water content resulting from channeling at single layer or bottom water coning that is caused by multi-layer development and powerful interlayer heterogeneity
Remaining oil saturation	The remaining oil has a relatively high saturation, with large potential
Water content of oil well	＞90%
Permeability of channeling layer	＜10000mD
Mineralization	＜200000ppm

Methods of Application

The chemical commingled plugging technology: Complete the fluid preparation on the ground, and then pump into the formation by plunger pump. After squeezing, replace the injection water, shut in for coagulation, start up the pump, produce at variable frequencies, produce in small displacement and then adjust the fluid production capacity according to the water content.

The staged packer plugging technology of horizontal well: move the string for operation, run down the squeezing string, inject the chemical packer materials at fixed points, lift out the squeezing string and replace with the water shutoff string, complete the plugging at fixed points, and then restore the production string of electric pump. Produce in small displacement when restoring the production, and then adjust the fluid production capacity according to the water content.

Application

The plugging operation has been implemented for 20 well-times in Bohai Oilfield and Nanhai Oilfield, with cumulative oil increases of 39,000t.

Case Study

Application case: A well in Bohai Oilfield

Development issue: The water channeling layer develops in the forth sand prevention section, and the production is stopped due to the water content of 100%;

Measuring effectiveness: The water content decreases from 100% to 20% at minimum, with oil production increased by more than 7,000t, and the oil well is resumed for production, with period of validity of more than 7 months.

Process Introduction

HGSC composite plugging removal technology, in collaboration with four functions of "generating heat chemically, increasing the energy by gas, chelation and dissolution, penetration cleaning", integrates the plugging removal concept of mechanical method, chemical method and thermal method organically, removes the organic plugging in the shaft and the immediate vicinity of wellbore resulting from the deposition of heavy components as well as the inorganic plugging caused by scaling of metal ions, releases the production capacity of oil well and improve its yield as well. This technology, which is mainly dominated by chemical heat generation system together with chelating system and organic cleaning system, could deal with organic and inorganic pollution at the same time, with the features of simple process, low costs, safe system, etc.

Technical Indicators

Technical Indicators；

Corrosion rate:＜1g/(m²•h);

With better compatibility, free from observed precipitation and flocculation.

Technical Applicability

Low producing wells once with high-yield period;

Wells plugged due to deposition of organic matters;

Applicable to medium and high porosity and permeability formation;

Water cut ≥40%

Supporting Systems, Software and Tools

This technology can cooperate with string operation, and support with hydraulic flushing nozzle for operations.

Inject parallel with two pumps, support with reaction inhibitor for operations.

Methods of Application

No special equipment required when operating, the process flow is as follows: (1) The slurry pump (acidizing pump) injects the front-placed slug; (2) Shut in for soaking; (3) the slurry pump (acidizing pump) injects the slug of HGSC-A+B as well as the slug of HGSC-C; (4) Shut in for soaking.

Application

HGSC composite plugging removal technology has been applied for more than 20 well-times in Bohai Oilfields from 2013 till now, with cumulative yield increased by 70,000t.

Case Study

The Well S-G5 in Bohai Oilfield began annular fluid replacement at the end of 2011, and has checked the pump 4 times from 2011 to 2013. There was no obvious effect through thermal washing, inverse well-flushing and other operations, with the fluid production capacity remained unchanged, an increase in water cut, so it was believed that the formation was polluted according to analysis.

The average daily fluid production was 48m3/d, daily oil production of 3.4m³/d before the HGSC composite plugging removal operations; the average daily fluid production was 74.5m³/d, daily oil production of 60.7m³/d, with significant stimulation effect.