3. Experiment on reducing viscosity of biological adhesive

(1) Experimental methods

Take 120mL of oil sample and place it in a container. Place the container containing the oil sample in a 50℃ water bath at a constant temperature. Take the sample and place it on a viscometer tray to measure the initial viscosity of the oil sample (viscosity without added medication).Then, gradually add 1.2mL (concentration 1%) and 2.4mL (concentration 2%) of bio gel to the oil sample, stir evenly, and maintain a constant temperature. Take the samples after each stage of dosing and place them in the viscosity meter tray to measure the viscosity of the oil sample after dosing.

(2) Evaluation method

Calculate the viscosity reduction rate based on the changes in viscosity before and after adding the oil sample. The higher the viscosity reduction rate, the better the effect. The indoor experimental data is shown in Table 2.

4. Biogel wax prevention experiment

(1) Experimental methods

The wax in crude oil precipitates as a solid, which is difficult to express in volume units, so the experiment uses mass units.Take one (100g) oil sample from each of the TXX-1 and TXX-6 wells and place them in two stainless steel cups. Use the same method to test the wax prevention rate of the oil samples from both wells.The experimental method is as follows: Two oil samples are not added with any chemicals first. The container containing the oil samples is placed in the ROFL-2009 fully automatic wax cleaning and anti waxing agent tester and kept at a constant temperature for 30 minutes. Then, the flowable oil sample is poured out, weighed, and recorded as m₁；Next, add 2% concentration of bio gel to the non flowing oil sample, place the container containing the oil sample into the fully automatic wax cleaning and anti waxing agent tester, maintain a constant temperature for 30 minutes, then pour out the flowable oil sample, weigh the remaining oil sample and record it as m₂；Calculate the wax prevention rate based on recorded data.

(2) Evaluation method

Calculate the wax prevention rate based on the remaining mass of the oil sample without or with added chemicals. The indoor experimental data is shown in Table 3.

                                           Note: Wax prevention rate=(m₁- m₂)/m₁×100%.

(3) Result analysis

The experimental results show that the wax prevention rate of bio gel can reach over 61% at a concentration of 2%.

5. Biogel emulsification experiment

(1) Experimental methods

① Take 70mL of crude oil into a beaker, add 30mL of water, maintain a constant temperature of 50℃, shake thoroughly, and observe the fusion of crude oil and water.

② Take 70mL of crude oil into a beaker, add 30mL of water, add 1% concentration bio gel, maintain a constant temperature of 50℃, shake thoroughly, and observe the fusion of crude oil and water.

(2) Evaluation method

Based on the fusion of the oil sample with and without biological collagen oil and water, the emulsification effect was observed. It was found that the crude oil and water were fully fused and the emulsification effect was good. The indoor experimental data is shown in Table 4.

(3) Result analysis

After adding bio gel, the oil and water fully blend and the emulsification effect is significant.

6. Oil washing experiment of bio adhesive viscosity reducer

(1) Experimental methods

① Add an appropriate amount of oil sand.

② Pour 50mL of oil-water single bottle into the beaker, and add 1% and 2% of bio gel to the beaker respectively.

(2) Evaluation method

Based on the sand washing conditions with and without the addition of bio gel in the oil sample, observe the sand washing effect. The cleaner the sand, the better the sand washing effect.

(3) Result analysis

The best oil washing effect is achieved by adding 2% bio gel viscosity reducer.

7. Experimental conclusion

This bio adhesive viscosity reducer uses emulsification, dispersion, and chain breaking methods to reduce the viscosity of heavy oil. The viscosity reduction effect varies under different oil-water ratios and dosages.Experiments have shown that adding 2% bio gel viscosity reducer can achieve a viscosity reduction rate of 95.0%, and the bio gel viscosity reducer has the best oil washing effect at a dosage of 2%. It is recommended that the user use a reasonable concentration ratio of biological glue based on the on-site situation.

Ⅴ. Field Test of Bio Adhesive Viscosity Reducer Fracturing

1. Biological adhesive viscosity reduction and sand fracturing

(1) Design of fracturing parameters for newly deployed evaluation wells in the periphery

① Fracturing method: For new wells that have not been fractured and newly used reservoirs close to heavy oil, a fracturing engineering method is adopted with the use of bio gel viscosity reducer technology.

② The physical properties of the reservoirs in the peripheral blocks of Fuyu Oilfield are poor, with low permeability. Based on the principle of "transforming complex fracture networks and increasing the contact area between fracturing fluid and matrix", the horizontal stress difference between the two directions is 0.4-0.6MPa.Based on the geological data of TXX-1 and TXX-6 wells, the minimum displacement of 4m³/min has been preliminarily optimized through stress analysis.Conduct on-site small-scale pre pressure testing and provide real-time interpretation of net pressure. According to the matching table of diversion capacity, the sand addition strength is designed to be greater than 5m³/m. Two types of particle size proppants are used, with 70-140 mesh to increase the proppant transport distance and 16-30 mesh to increase the diversion capacity of the main crack. The sand addition amount for Interpretation Layer 11 is 10m³ (3+7), and for Interpretation Layer 8 it is 15m³ (5+10), as shown in Table 5.

The fracturing technology parameters adopt a flow rate of 4m³/min, and the same flow rate is used for the main crack of the frozen gel. After supporting the main crack, hot water is used to prepare a viscosity reducer (with a concentration of 1%), and a flow rate of 5m³/min is pumped in to increase the volume affected by the viscosity reducer and reduce the viscosity and coagulation of the fluid. Based on previous experiments, the injection of viscosity reducing agent liquid with a strength of 15-20m³/m will be carried out. After the completion of this stage of construction, the flow rate will continue to be increased to create cracks and sand support, fully supporting the branching cracks after increasing the flow rate.

(2) Brief summary

From 2022 to 2023, 24 evaluation wells and new wells will be deployed in the periphery, with a designed production capacity of 0.6t/d; The fracturing process of pre fracturing with guar gum, proppant, bio gel viscosity reducer, proppant, and post fracturing with liquid viscosity reducer was adopted, and the average daily production of a single well reached 2t/d in the initial stage, achieving efficient development of peripheral blocks.

2. Biogel viscosity reduction without sand fracturing

For wells near heavy oil blocks with repeated fracturing or significant viscosity increase, if the oil flow channel is blocked due to the increase in crude oil viscosity, resulting in a decrease in production, no sand and viscosity reduction fracturing tests shall be conducted.

① Based on the analysis of the previously selected well layer transformation volume and the injection production relationship of this layer, the total fluid consumption for this viscosity reduction without sand fracturing is calculated. Generally, it is 1.2 to 2 times the volume of the previous transformation multiplied by the transformation volume (the largest transformation volume in previous times is the standard). The transformation volume=crack length x crack width x crack height.

② The fracturing ability of bio gel without sand to reduce viscosity is weaker than that of conventional fracturing fluid with proppants. Therefore, when using bio gel as fracturing fluid, the construction displacement should be 1.5 to 2 times that of previous fracturing.First, pump in the bio gel that matches the properties of the crude oil in this block, with a construction displacement of 1.5 times the conventional fracturing displacement. By injecting bio gel at high speed, it comes into contact with the high viscosity crude oil adsorbed on the rock surface and in contact with the supporting agent in the supporting cracks, reducing its viscosity, dissolving wax and gum, improving the permeability of the oil phase and the flowability of the crude oil, thereby enhancing the flow capacity formed by the original fracturing transformation.

Ⅵ. On Site Application Effect

The technology of reducing viscosity with sand fracturing and the technology of reducing viscosity without sand fracturing have been implemented in 45 wells in the periphery of Fuyu and heavy oil blocks, achieving good application results.

① The technology method of creating main cracks+proppant+bio adhesive viscosity reducer+proppant+viscosity reducer has been applied in the newly put into operation peripheral and heavy oil blocks, with obvious application effects. A total of 5 wells have been implemented. 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.

② The non sand viscosity reduction 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. A total of 40 wells have been implemented, and under the same conditions, the viscosity has decreased from 70mPa·s before fracturing to 25mPa·s. The increase in production is 1.3 times that of conventional fracturing in the same block, and the efficiency is increased by 10 percentage points.

Ⅶ. Conclusions

① A composite bio gel formulation system has been developed to address the difficulties in the development of peripheral blocks in Fuyu Oilfield. It has good compatibility with peripheral reservoirs and can effectively reduce crude oil viscosity, pour point, and improve oil recovery efficiency.

② Combining different geological characteristics and fracturing well history conditions, the fracturing engineering supporting technology for Fuyu Old Oilfield under different geological characteristics has been formed by adopting the construction process of fracturing+support+bio gel viscosity reduction+support+post bio gel viscosity reduction, and bio gel viscosity reduction without sand fracturing.