——Application of the technical method of using pre liquid guanidine gum to create main cracks, proppant, bio gel viscosity reducer, proppant, and post liquid viscosity reducer

Abstract

The crude oil density, viscosity, solidification point, and wax content in the peripheral blocks of Fuyu Oilfield are high, and conventional guar gum sand carrying fracturing technology cannot effectively exploit them. After fracturing and production, the initial output is low, and the effective production capacity cannot be achieved. The peripheral blocks are basically undeveloped and unused.To this end, a viscosity reducing fracturing technology was developed that is compatible with the bio gel viscosity reducing agent system and fracturing engineering technology, and experimental evaluations were conducted. The evaluation results show that the bio gel has properties such as pour point reduction, viscosity reduction, wax prevention, emulsification, and oil displacement, which can significantly improve the fluidity of crude oil.The on-site test is divided into two technical methods: bio gel viscosity reduction with sand fracturing and bio gel viscosity reduction without sand fracturing. A total of 45 wells have been implemented in the periphery of Fuyu and heavy oil blocks.The technical method of using pre liquid guar gum to create main fractures, proppant, bio gel viscosity reducer, proppant, and post liquid viscosity reducer has been applied in the newly put into operation peripheral and heavy oil blocks. Compared with the old area, under the condition of deteriorating reservoir properties, the oil production after production exceeded the design capacity by 1.6 times, which is 1.4 times that of the old area.The bio gel viscosity reduction without sand fracturing technology is mainly applied in the secondary fracturing of old wells or multiple rounds of fracturing of heavy oil blocks or viscosity rising well layers. Under the same conditions, the viscosity decreases from 70mPa · s before fracturing to 25mPa · s, and the production increase is 1.3 times that of conventional fracturing in the same block.

Ⅰ. Introduction

Fuyu Oilfield has been developed for more than 60 years, ith a daily oil production of 0.2-0.3t/d per well and a comprehensive water content of 96%. It is difficult to achieve stable water injection production.To achieve stable and increased production in old oil fields, the effective utilization of peripheral proven reserves is of great significance. The peripheral reserve blocks of Fuyu Oilfield have not been developed and utilized for a long time before 2022 due to the inability to achieve effective production capacity after fracturing and production.Since 2022, in response to the problem of difficult access to peripheral reserves, a "bio gel viscosity reducing agent system" and fracturing engineering technology have been studied to develop viscosity reducing fracturing technology. 24 wells have been implemented in peripheral block mines, and after fracturing and production, the daily oil production of each well has reached more than 2t/d, promoting further effective utilization of peripheral reserves in Fuyu Oilfield.Improving the fracturing effect on unused peripheral reserves, high viscosity (condensate) oil, and near heavy oil reservoirs in other old oil fields has a good guiding role and prospects for field application.

Ⅱ. Basic Geological Characteristics of Peripheral Blocks in Fuyu Oilfield

The peripheral blocks of Fuyu Oilfield are cut by three nearly north-south normal faults, forming two relatively independent fault structures.The top structure of the Quansi section has an elevation of -270 to -320 meters, and the oil reservoir is buried at a depth of 390 to 490 meters. The development layer is the Fuyu oil layer of the Quansi section deposited in river facies. The main body of Fuyu Oilfield belongs to structural oil reservoirs, while its peripheral blocks belong to lithological fault block structural oil reservoirs.The thickness of the Fuyu oil layer in Quansi section is 90-100m, and the stratigraphic correlation is divided into 4 sets of sand formations, with 12-13 sub layers. The main oil layers are the 9th and 10th sub layers (3-4 sand formations), with locally developed 2nd and 3rd sub layers (1 sand formation) and 6th and 7th sub layers (2 sand formations). The average sandstone thickness of Fuyu oil reservoir is 30.9m, the average effective thickness is 10.2m, the porosity of the reservoir is 25%, and the permeability is (40-100) × 10^-3 μm².

The surface crude oil in this block is brown black in color, characterized by high relative density, high viscosity, high freezing point, and high wax content. The temperature of the oil reservoir is 20-25℃, and the viscosity of the surface degassed crude oil is 60-80mPa·s at 50℃. Under the formation conditions of 30℃, the viscosity reaches 180-400mPa·s, the solidification point is 17.8℃, the wax content is 13.8%, and the average crude oil density is 0.877g/cm³.According to the natural gas composition analysis report of 10 wells in Fuyu Oilfield, the dissolved gas is mainly methane, containing small amounts of chlorine, ethane, nitrogen, propane, butane, pentane, hydrogen sulfide, and carbon dioxide.The total mineralization degree of the formation water is 4000-6000mg/L, the pH value is 7-8, and the water type is NaHCO₃. The original formation pressure is 4.2MPa and the saturation pressure is 3.6MPa. The new wells deployed in 2015 adopted conventional fracturing, with low initial production and inability to achieve effective production capacity, resulting in the cessation of use. The peripheral blocks are basically undeveloped and unused.

Ⅲ. The Problems faced by Conventional Fracturing Technology

1. The conventional fracturing production increase in the periphery of Fuyu is low

Before 2015, four new oil wells were deployed in the peripheral blocks, using conventional guar gum sand carrying fracturing technology. The initial average single well production capacity was relatively low, 0.6 t/d lower than the designed production capacity.

2. Analysis of the Inefficient Reasons for Conventional Fracturing Technology

In the development process of most heavy oil reservoirs in China, due to the influence of crude oil viscosity, the flowability of crude oil is poor, and steam flooding and other development modes are generally adopted. Under conventional fracturing conditions, oil producing wells in high viscosity (condensate) oil reservoirs or near heavy oil reservoirs have lower daily oil production levels, faster water content increase rates, and poorer fracturing effects due to the influence of crude oil fluidity.

For conventional oil reservoirs developed on land, with the extension of water injection development years, the viscosity and freezing point of the crude oil show an increasing trend. The viscosity of the crude oil in the lower part of the structure is even higher, and the flowability of the crude oil adhered to the rock surface, pores, and proppant contact surfaces is poor, thereby reducing oil production.The conventional fracturing engineering techniques for oil reservoirs generally do not consider the impact of crude oil viscosity on production, and mainly aim to improve diversion and permeability. It is not possible to increase fracturing production by reducing crude oil viscosity.

Based on the understanding of heavy oil block development engineering technology, as well as the analysis of fracturing effects in high viscosity (pour point) oil reservoirs and near heavy oil reservoirs, in order to solve the problems of poor fracturing effects in high viscosity (pour point) oil reservoirs or near heavy oil reservoirs and the increase in crude oil viscosity in water injection areas, it is urgent to develop a fracturing technology approach and fracturing materials for such reservoirs, which can not only improve the fracturing production effect, but also reduce costs, and the fracturing fluid materials should achieve pollution-free and environmentally friendly effects. Provide strong assistance and effective technical support for the efficient development and utilization of high viscosity (condensate) oil reservoirs or near heavy oil reservoirs.

Ⅳ.The bio adhesive viscosity reduction system can effectively improve the flowability of crude oil

1. Biogel Viscosity Reducer System

A bio gel viscosity reducer with various properties such as pour point reduction, viscosity reduction, wax prevention, emulsification, and oil displacement has been developed to address the problem of difficulty in extracting oil from areas close to heavy oil reservoirs and high viscosity (pour point) oil containing blocks due to high crude oil viscosity and solidification point. This can provide strong technical support for increasing production and production in new and old oil fields.Its basic principle is: through the action of bio glue, the high viscous substances in crude oil are dispersed to form oil in water lotion, which changes the rock wettability, reduces the mobility ratio, and thus improves oil recovery.

(1) Formula and ratio of bio gel products

Protease 0.5%~5.0%+amylase 0.5%~5.0%+lipase 0.2%~6.0%+cellulase 0.3%~3.0%+complex amylase 0.5%~7.0%+fungicide 0.5%~5.0%+water (balance 92%~63.5%)+stabilizer 5%+polyacrylamide 0.5%.

(2) Preparation method of bio gel

Step 1: Add 0.2% to 1.0% protease+0.5% to 5.0% amylase+0.2% to 2.0% lipase+0.3% to 3.0% cellulase+0.3% to 3.0% composite amylase to water according to the specified content and composition, and stir to dissolve.

Step 2: Add 0.5% to 5.0% antibacterial agent and 5.0% stabilizer to the solution formed in Step 1, stir and mix evenly. Step 3: Add deionized water and 0.5% polyacrylamide to the solution formed in Step 2 until the total component percentage reaches 100%, stir evenly to obtain the bio gel.

2. Evaluation of biological gel pour point reduction

(1) Experimental methods

Put 80mL of crude oil into two dedicated measuring cylinders, one without adding any chemicals, and gradually add 0.8mL (1%) and 1.6mL (2%) of bio gel to the other. Place the measuring cylinder into the TP6 pour point meter, set the temperature, insert a thermometer, gradually cool down, and observe the flow of crude oil.

(2) Evaluation Method

Gradually cool the oil sample with and without bio gel from 70℃, observe the flow of the crude oil, and determine the pour point of the crude oil. The indoor experimental data is shown in Table 1.

(3) Result Analysis

The experimental results of different concentrations of bio gel show that the pour point reduction effect is better at a concentration of 2%, and this bio gel meets the pour point reduction requirements of oil wells in the peripheral blocks of Fuyu Oilfield.In different application environments, the optimal on-site application conditions can be achieved by adjusting the dosage of the medication. When the crude oil variety changes, it is necessary to adjust and optimize the product formula, and iteratively upgrade the product performance.