Process Introduction

The long well section of horizontal well is made with a number of hydraulic fractures by staged fracturing, then discharge the fluid rapidly after fracturing, and transform the reservoir by staged fracturing of horizontal well efficiently with low damages, thus improving the production of a single well as well as achieving the target of improving the yield. The technical difficulty of fracturing lies in the selection of staged fracturing technology. The most commonly used technology includes the staged fracturing by openhole packers and by hydraulic jet, etc.

Technical Indicators

Technology Type	Staged fracturing by openhole packers	Staged fracturing by hydraulic jet
Technical Indicators	1. Resistance to pressure of 70MPa, temperature resistance of 170℃； 2. Maximum number of transformed sections of 20 (vary according to the size of string).	1. Operating pressure differential ≤ 60MPa; 2. Pressure drop of nozzle ≤ 40MPa.

Technical Applicability

The staged fracturing of horizontal well by openhole packers is applicable to the stimulation and reconstruction of a wide range of oil-gas wells, and this technology is simple, low in costs and time-saving. Currently, this technology has been widely used on land oilfields and offshore oilfields, with significant stimulation efficiency.

The staged fracturing technology by hydraulic jet is applicable to open-hole completion, screen pipe completion and cased hole completion, and its applicable well depth is less than 5000m. This process does not require lifting or running the string frequently, simplifies the process, saves the construction time; the down-hole tool string is simply, with high security, and the entire process does not require the mechanical packing device, and could reduce the operational risks and costs.

Supporting Systems, Software and Tools

Application

The horizontal well of tight sand gas has tested for 7 well-times by adopting the staged fracturing by openhole packers, with the fracturing stimulation 10 times better more than that of vertical well and the directional well in terms of the open flow capacity after the fracturing, with obvious stimulation effect.

Well Name	Date	Open Flow Capacity,104m3/d
A-1H	2016.9	2.85
A-4H	2016.11	4.8
A-5H	2016.11	18.3
B-3H	2016.8	4.71
A-3H	2016.06	7.6
B-1H	2016.11	2.43
C1-H	2015.11	9.2

Case Study

The Well A-1H in Bohai Oilfield, with low penetration probability of sandbody, whose horizontal section is divided into 7 sections according to its lithology, physical property, electric index, etc., six of which indicate to be mudstone or sandy mudstone, with fault developing near the horizontal segments, may face the construction risks that the formation cannot be opened by pressure, difficulties in sand adding, etc. The open-hole packer of staged fracturing tools is run down to optimize the position of sliding sleeve, reduce the ratio of sand in mud stone section, and the open flow capacity is up to 110,000 cubic meters/day, with obvious stimulation effect.

Process Introduction

Technical Indicators

Technical Applicability

In terms of the low-permeability oilfields recovered by multi-layered system, the reservoir profile and plane are seriously heterogeneous, with great differences between layers, the combined fracturing would result in uneven reservoir reconstruction and sand plugging after fracturing, while the layered fracturing string of packer could be separated manually, which could avoid contacting the edge and bottom water, coal bed and fault while improving the construction efficiency and success rate significantly so as to reconstruct the reservoir thoroughly.

The fracturing technology of separate layers by packers is applicable to the vertical wells and directional wells, with well temperature of ≤100℃, and construction pressure of ≤70MPa.

Supporting Systems, Software and Tools

Application

The tight sand gas site has utilized the layered fracturing technology for vertical and directional wells to test on site for 2 well-times since 2013, which fractures 4 layers continuously without moving the string successfully. The combined recovery capacity is up to 16,000 cubic meters/day after fracturing, with an obvious stimulation effect, and the time efficiency of single well is increased by 75%.

Case Study

The Well A-8 is a development well, and in order to develop by multi-layer system and transform the vertical reservoir evenly, the K344 packer + hydraulic anchor + sliding sleeve + string with safety joints are used to construct the two layers, after which the yield is increased to 61,000 cubic meters/day from 7,000 cubic meters/day before the fracturing, so the operating time-efficiency of a single well is improved significantly.

Process Introduction

The fracturing testing integration technology is a technique that completes the perforation, routine testing and fracturing construction at one-off string in the fracturing development of oil-gas oilfields. Such string is utilized to reduce the secondary pollution to the formation by killing fluid, and could compare the fracturing results before and after the transformation.

Technical Indicators

Technical Applicability

The fracturing testing integration technology is applicable to the fracturing transformation of exploration wells requiring routine tests, which can be used to compare the results obtained before and after such transformation; also applicable to low-permeability gas well in particular, which is demanding for down-hole operation technology, with large difficulty in implementation and higher construction costs.

Application

Currently, this technology has been applied successfully on the sea for 8 well-times, which lowered the cost of fracturing operations, and achieved better economic benefits as well.

Case Study

Process Introduction

The low-temperature fresh water based fracturing fluid is a water-base gel fracturing fluid based on low-concentration guar gum, and the densifier refers to the low concentration hydroxypropyl guar gum, with low residue contents. According to the low porosity, low permeability, low pressure and lower temperature feature of the low-permeability reservoir and tight sand gas reservoir, this fracturing fluid system solves the problems of high residue contents in regular fracturing fluid, unthorough gel breaking at low temperature, low efficiency in flow-back and serious damages to water lock.

The low-temperature fresh water based fracturing fluid system is featured with: powerful solid-carrying capacity, thorough gel breaking under low temperature condition, high anti-swelling rate, ultra-low surface tension, high flow-back efficiency and outstanding reservoir protection performance.

Technical Indicators

No.	Items		Industry Standard	System Index
1	Apparent viscosity of base fluid, mPa • s		10~40	16~22
2	Crosslinking time, s		15～60	30~60
3	Capacity of resistance to high temperature and shearing	Apparent viscosity, mPa • s	≥50	160
4	Static filtration-loss performance	Filtration-loss coefficient, m • min-1/2	≤1.0×10-3	6.9 ×10-4
		Filtration-loss rate, m/min	≤1.5×10-4	1.15×10-4
5	Gel breaking time, min		≤720	60~240
6	Residue content, mg/L		≤600	148
7	Surface tension, mN/m		≤28.0	18.6
8	Matrix permeability damage ratio, %		≤30	16~22

Technical Applicability

Application

The low-temperature fresh water based fracturing fluid system has been implemented successfully for 96 well-times in the fracturing of tight gas fields since 2013 to 2016.

Case Study

A total of 40.0 cubic meters of sand are added for the fracturing of this well, and the open flow capacity of the tested producing gas is more than 150,000 cubic meters/day after the fracturing.

Well No.	Temperature, ℃		Permeability, mD	Porosity, %	Shale content, %
X-3	47		0.29	6.4	5.9

Process Introduction

The high-temperature fresh water based fracturing fluid system consists of the guar gum, the high-temperature cross-linking agent, the temperature stabilizer and other additives, which is featured with better resistance to temperature and shearing, better stability, powerful solid-carrying capacity, high temperature resistance, controllable delay time of crosslinking; controllable gel breaking time, thorough gel breaking, low residue and outstanding reservoir protection performance. This system is applicable to the fracturing of high-temperature (120~160℃) deep oil-gas wells.

Technical Indicators

No.	Items		Industry Standard	System Index
1	Apparent viscosity of base fluid, mPa • s		30~100	94
2	Crosslinking time, s		60~300	120
3	Capacity of resistance to high temperature and shearing	Apparent viscosity, mPa • s	≥50	66(160℃)
4	Matrix permeability damage ratio, %		≤30	22
5	Gel breaking performance	Gel breaking time, min	≤720	120~240
		Gel breaking time, min	≤5	3.5
		Surface tension of gel breaking fluid, mN/m	≤28	22.9
		Interfacial tension between gel breaking fluid and kerosene, mN/m	≤2	1.81
6	Residue content, mg/L		≤600	355
7	Demulsification ratio, %		≤95	99
8	Resistance-reducing ratio, %		≥50	51.3

Technical Applicability

Applicable to the temperature range of reservoir: 120℃＜T＜160℃; applicable to deep hydrocarbon reservoir.

Application

The high-temperature fresh water based fracturing fluid system has been implemented successfully for 13 well-times in the fracturing of offshore tight gas fields since 2010 to 2015.

Case Study

A total of 35.0 cubic meters of sand are added for the fracturing of this well, and the tested daily gas yield reaches more than 90,000 cubic meters/day after the fracturing.

Well No.	Temperature, ℃		Depth, m	Permeability, mD	Porosity, %	Shale content, %
X2-x-1	150		3979.7	2.1	10.4	3.8

Process Introduction

The sea water based fracturing fluid system consists of salt-tolerance thickener, high-temperature salt-resistance cross-linking agent, gel protestant and other additives, which is prepared directly by filtered sea water, characterized by powerful capacity in salt resistance, resistance to high temperature, better solid-carrying capacity, outstanding performance in reservoir protection, continuous mixing, etc.

Technical Indicators

No.	Items		Industry Standard	System Index
1	Apparent viscosity of base fluid, mPa • s	20℃＜T＜60℃	10~40	27
		60℃＜T＜120℃	20~80	35
		120℃＜T＜180℃	30~100	100
2	Crosslinking time, s	20℃＜T＜60℃	15~60	50
		60℃＜T＜120℃	30~120	70
		120℃＜T＜180℃	60~300	120
3	Capacity of resistance to high temperature and shearing	Apparent viscosity, mPa • s	≥50	57(170℃)
4	Matrix permeability damage ratio, %		≤30	24
5	Gel breaking performance	Gel breaking time, min	≤720	120~240
		Apparent viscosity of gel breaking fluid, mPa•s	≤5	2.9
		Surface tension of gel breaking fluid, mN/m	≤28	25.6
		nterfacial tension between gel breaking fluid and kerosene, mN/m	≤2	1.7
6	Residue content, mg/L		≤600	283
7	Demulsification ratio, %		≤95	99
8	Resistance-reducing ratio, %		≥50	52.8

Technical Applicability

The sea water based fracturing fluid system is applicable to the temperature range of reservoir: 20℃＜T＜170℃; and also applicable to the fracturing of offshore oil-gas well and fracturing-packing operations.

Application

The sea water based fracturing fluid system is used to test 1 well on site, with better application performance obtained. This well is added with 40.0 cubic meters of sand for fracturing, working fluid of 565.0 cubic meters, and the fracturing task is completed successfully, and fluid performance could meet the requirements for the fracturing of high-temperature deep wells.

Process Introduction

The high-temperature clean fracturing fluid is characterized by low residue, low damages, resistance to high temperature and low friction, with outstanding reservoir protection performance.

Technical Indicators

No.	Items		Industry Standard	System Index
1	Thickening time, s	20℃＜T＜60℃	15~60	50
		20℃＜T＜60℃	30~120	90
		120℃≤T＜180℃	60~300	120
2	Capacity of resistance to high temperature and shearing	Apparent viscosity, mPa•s	≥50	58(140℃)
3	Visco-elasticity	Storage modulus, Pa	≥2.0	3.5
4		Storage modulus, Pa	≥0.3	1.5
5	Matrix permeability damage ratio, %		≤20	15.71
6	Gel breaking performance	Gel breaking time, min	≤720	90~150
		Viscosity of gel breaking fluid, mPa•s	≤5	4.2
7	Residue content, mg/L		≤100	0
8	Resistance-reducing ratio, %		≥50	56

Technical Applicability

It is applicable to the temperature range of reservoir: 20℃＜T＜140℃; applicable to the fracturing of oil-water well and fracturing-packing operations. The high-temperature clean fracturing fluid is characterized by better resistance to high temperature and outstanding reservoir protection performance, with broad application prospects.