(China Petroleum Exploration and Development Research Institute, Beijing 100083)
Emulsion polymer was synthesized by inverse microemulsion polymerization, and indoor performance evaluation, pilot scale-up test and field test were carried out. The results show that emulsion polymer is easily soluble in water and can be directly added into positively charged drilling fluid, which can effectively shorten the hydration and slurry preparation time in the field. As a drilling fluid additive, emulsion polymer has good viscosity increasing, filtration loss reducing and water loss reducing properties. When the dosage of emulsion polymer is 0.4%, it can meet the basic requirements of drilling fluid performance. The production route is reliable, the product performance is stable, and the production can be expanded; The application of emulsion polymer in positively charged drilling fluid has achieved ideal application results in the field test of Dagu 1 well.
Microemulsion polymerization; Emulsion polymer; Synthesis of positive charge drilling fluid
Application of emulsion polymer in positively charged drilling fluid
Lin, Ming, Zhi, Wang Lin
(Petroleum Exploration and Development Research Institute, Beijing 100083)
An emulsion polymer was synthesized by microemulsion polymerization. The indoor performance evaluation, pilot-scale synthesis and field application of emulsion polymer were studied. The results show that emulsion polymer is easily soluble in water and can be directly added into drilling fluid, which effectively shortens the preparation time of drilling fluid. As a drilling fluid additive, emulsion polymer has good properties of increasing viscosity, enhancing shear and reducing filtration loss. When the concentration of emulsion polymer is 0.4%, it can meet the basic requirements of drilling fluid performance. Good field application results have been achieved in Dadu 1 well.
Keywords microemulsion polymerization emulsion polymer synthesis of positive drilling fluid
At present, the product form of polyacrylamide used in oil fields in China is basically powder, and large-scale dissolution devices are needed for field application. Moreover, the production process of polyacrylamide is bulk adiabatic kettle solution polymerization introduced from China in the 1990s, with low mass fraction of polymerization solution and relatively small molecular weight of the product. In the process of making dry powder, high temperature drying and shearing are easy to degrade and cross-link polymer chains, which makes the solubility and flocculation of powder products worse.
Emulsion polymerization is also a widely used polymerization method in industry. The molecular weight of emulsion polymerization products is higher than that of solution polymers. Polymerization products are generated in the form of latex, and if they are directly used in the form of latex, the operation is easier; Emulsion polymerization also has some other advantages, such as easy transfer of polymerization heat, high polymerization rate and easy control of product molecular weight. Because of these unique advantages, the development of emulsion polymerization technology has attracted the attention of many researchers. Since the French scientist Candau [1] first obtained stable, high molecular weight and narrow distribution polyacrylamide inverse microemulsion by inverse microemulsion polymerization in 1980s, scholars at home and abroad have done a lot of research on inverse microemulsion polymerization of acrylamide [2 ~ 4]. At present, only Cytec company has obtained the patent right of inverse microemulsion polymerization of polyacrylamide, and most of the domestic research is in the laboratory stage, which is far from industrial production. In this paper, polyacrylamide emulsion products which can be directly used as drilling fluid additives were synthesized by inverse microemulsion polymerization, and the indoor synthesis method, emulsion polymer properties and pilot test were discussed. The positive drilling fluid prepared with it as the main agent was tested in Dagu 1 well, No.2 structure in Dalaoba, Xinjiang.
Synthesis of 1 emulsion polymer
The main raw materials: acrylamide, acrylic acid, potassium hydroxide, nonionic surfactant, deionized water and white oil are all industrial grade, and initiator, ethanol and heptane are analytical pure reagents, high-purity nitrogen and phase inversion agent.
Synthesis process: In a four-necked flask (250mL) equipped with a constant pressure feeder, stirrer, thermometer and vent pipe, emulsifier and white oil were added and heated to dissolve. At the same time, acrylamide and potassium acrylate solution were added to the feeder. Add initiator before emulsification, stir and emulsify, and introduce nitrogen for 20min. Control a certain reaction temperature until the reaction conversion is completed.
Polymerization reaction formula:
Oil and gas accumulation theory and exploration and development technology
The emulsion polymer was fractionated with ethanol, and the white powder obtained after drying was ground in heptane and stirred for 24 hours. The filter cake was dried in vacuum and used for molecular weight determination. The viscosity-average molecular weight of emulsion polymer was 7.7× 106 measured by intrinsic viscosity method.
Properties of two emulsion polymers
2. Water solubility of1emulsion polymer
Adding emulsion polymer 1.0g into 200mL water with stirring, the emulsion polymer dispersed rapidly in the experiment, and the complete dissolution time was less than 2min. It can be seen that the emulsion polymer drilling fluid additive is easily soluble in water and can be directly added to the drilling fluid for use, which shortens the hydration and slurry preparation time in the field and achieves the expected effect in a very short time.
2.2 Influence of emulsion polymer on drilling fluid performance
Taking 4% bentonite slurry as base slurry, add emulsion polymer to the base slurry, and stir the drilling fluid at high speed for 65438 00 minutes. The rheological properties of drilling fluid were tested by rotary viscometer. According to the petroleum industry standard SY/T562 1-93, the API filtration was measured with ZNS- 1 medium pressure mud filtration tester.
See table 1 for the influence of emulsion polymer on drilling fluid performance. The results show that the addition of emulsion polymer can improve the apparent viscosity and dynamic shear force of drilling fluid and reduce water loss. When the dosage of emulsion polymer is 0.4%, it can meet the basic requirements of drilling fluid performance and meet the needs of upper drilling engineering.
Table 1 Effect of emulsion polymer on drilling fluid performance
2.3 Salt resistance of emulsion polymer
Add 1.2% emulsion polymer to the base slurry with different sodium chloride dosage to test the drilling fluid performance. The results are shown in Table 2. It can be seen that the emulsion polymer has a strong resistance to sodium salt, and it shows a good effect of increasing viscosity and reducing water loss when the dosage is small. It is suitable for drilling and oil displacement in high salinity strata.
Table 2 Salt tolerance of emulsion polymers
3 pilot scale-up test of emulsion polymer
Due to many factors affecting inverse emulsion polymerization, on the basis of optimizing the synthesis process, the stability of the synthesis process was investigated with domestic industrial products as raw materials, and the industrialization of polymer synthesis was explored. Eight batches of samples were synthesized and the properties of all products were tested. Table 3 shows the intrinsic viscosity and viscosity-average molecular weight of the emulsion polymer. The viscosity-average molecular weight of all products was stable, and kept at 4./kloc-0 /×106 ~1.5×107.
Table 3 Intrinsic Viscosity and viscosity-average molecular weight of Emulsion Polymer
Add emulsion polymer into drilling fluid base slurry, stir at high speed for 65438±00min, and test the rheological property of drilling fluid with rotary viscometer. According to the petroleum industry standard SY/T562 1-93, the API filtration was measured with ZNS- 1 medium pressure mud filtration tester. Table 4 shows the influence of emulsion polymer on drilling fluid performance. It can be seen that in 20% sodium chloride brine drilling fluid, all emulsion polymers can effectively reduce the filtration loss of drilling fluid and significantly improve the plastic viscosity of drilling fluid. It can be seen that the process route is mature and stable, which can expand production and lay a good foundation for field pilot test.
Table 4 Effect of emulsion polymer on drilling fluid performance
Note: 1. Basic slurry composition: 5% bentonite with high slurry making rate +0.3% sodium carbonate +20% sodium chloride; 2.0.4% is the effective content of emulsion polymer.
4 field test
4. 1 dagu 1 well profile
Dagu 1 well is the first difficult and key pre-exploration well deployed by Northwest Branch of China Petrochemical Company in 2006 in the field of carbonate natural gas exploration of South Paleozoic in Tianshan Mountains. The design well is 6400 meters deep, and the target strata are Ordovician and CAMBRIAN. It is difficult to drill in this block, not only will it encounter high-pressure brine layer, but also the geological situation of the target layer is more complicated.
The test horizons are Neogene Jidike Formation, Paleogene Suweiyi Formation, Qomgram Group and Cretaceous. Test interval: 4450~5900m m, when drilling this formation, gypsum mudstone and sand mudstone develop, which is prone to collapse and sticking, especially the existence of high-pressure brine layer in Jidike formation, which puts forward higher requirements for drilling fluid performance maintenance.
Main treatment agents for Dagu 1 Well: KPAM, NH4PAN, WFT-666, SMP-2, SPNH, CXP-2 and GMP-3. Positive additives: emulsified paraffin (RHJ- 1) and emulsion polymer (DS-30 1).
4.2 Indoor testing
In order to observe the influence of emulsion polymer DS-30 1 on the performance of field drilling fluid, an evaluation experiment on the influence of emulsion polymer on the performance of well slurry was carried out (Table 5). The results show that 0.3%DS-30 1 slightly increases the plastic viscosity and dynamic shear force of the original drilling fluid at room temperature, and the instantaneous water loss increases but has little effect on API water loss, so it can be put into well testing.
Table 5 Effect of emulsion polymer DS-30 1 on cement slurry performance
Note: 1. T in the table? Time of outflow of water loss in the medium-pressure water loss experiment, in seconds (s); 2. Other properties of experimental well mud are as follows: density is 1.56kg/L, pH value is 8.5, Vs is 2 1.8%, and Vb is 39g/L; 3. The experimental process is 6000r/min, and the performance is measured by high-speed stirring for 20 minutes.
4.3 Well entry test
Dagu 1 well is the key exploration well in China Petrochemical Company. The purpose of drilling is to find and protect oil and gas reservoirs. According to the new logging standard (or specification), the total hydrocarbon content (reference value) must be controlled within 0.5%. After this value is exceeded, drilling must be stopped to treat drilling fluid. Add 100 kg DS-30 1 slowly according to the cycle. The total hydrocarbon value of drilling fluid before adding is 0. 15%, and the maximum total hydrocarbon value of drilling fluid after 1.5 cycles is 0.17%; When the contrast is not too strong, the funnel viscosity of drilling fluid increases by 2s, and PV and YP have a slightly increasing trend. From the comparative experiment, it is found that after adding DS-30 1, the instantaneous water loss of drilling fluid increases, but the water loss of drilling fluid API changes little.
4.4 Application effect
(1) The drilling fluid coating has strong inhibition, good cuttings formation and sharp edges. See Figure 1 for the photo of cuttings in the second spudding of Dagu 1 Well. It can be seen that Dagu 1 well has good anti-collapse inhibition, which makes the mud logging cuttings returned during the whole second spudding construction very clear and well formed, and the cutting trace of PDC bit has hardly changed.
Figure 1 Dagu 1 Photo of drilling cuttings in the second spudding of Well.
(2) Short tripping and tripping are extremely stable without jamming. During the second spudding of Dagu 1 well, the interval of 2300 ~ 4964 m was always shortened 17 times, and every short trip was unimpeded, without any blockage, and the bottom speed of the next short trip was 100%. It fully shows that the second spudding drilling fluid has good rock carrying effect and good lubricity.
(3) The drilling fluid has strong anti-pollution ability, and has successfully passed through several sets of pure gypsum layers and high-pressure brine layers. Photo of cuttings in Dagu 1 Well 4802m is shown in Figure 2. According to the actual drilling data and geological logging analysis, the second spudding of Dagu 1 well encountered two possible high-pressure saline beds, namely, the interval of 4746 ~ 4748 m and the interval of 4859 ~ 4860 m; Three sets of gypsum layers with high purity were drilled: 4754 ~ 4756 m, 4800 ~ 4802 m and 4820 ~ 4822 m, and the pure gypsum content reached 50% ~ 70%. Especially after 45 14m enters the large section of gypsum mudstone, the dosage of salt-resistant and calcium-resistant treatment agent increases, and the drilling fluid performance remains relatively stable.
Fig. 2 Photo of 4802m cuttings from Dagu 1 Well.
(4) The drilling diameter is very regular and the drilling quality is excellent. The diameter curve of Dagu 1 well second spudding logging is shown in Figure 3. Figure 3 shows that the maximum hole diameter of φ3 1 1mm bit is 353mm, the minimum hole diameter is 278mm, the average hole diameter is 329mm, and the average hole diameter enlargement rate is 5.76%. There is no "big belly" interval in the whole second spudding, which fully shows that the drilling fluid in this interval has strong anti-collapse inhibition and the drilling fluid and drilling engineering construction measures are in place. The well diameter curve of Dagu 1 well third spudding is shown in Figure 4. According to the statistical analysis of the third spudding hole diameter of Dagu 1 Well, the average hole diameter enlargement rate of the third spudding is 3.03%.
Fig. 3 Diameter curve of Dagu 1 well second spudding
Fig. 4 Diameter curve of third spudding in Dagu 1 Well
① 1 inch = 0.0254m..
(5) The drilling fluid is clean, and the drill bit and centralizer are free of mud bags. During the second spudding of Dagu 1 Well, a total of 1 roller bit and 2 PDC bits (1 DBS and 1 Barrett bit) were used for 5 times of drilling. Don't trip out because of drilling fluid problems. There is no mud bag at the bit, centralizer and drill pipe joint every trip. This just shows that the drilling fluid has good rock carrying effect and clean drilling fluid.
(6) The total hydrocarbon value and fluorescence level are well controlled. During the whole drilling process of the second spudding and the third spudding, the total hydrocarbon value and fluorescence level of the treatment agent entering the well are closely monitored, and the dosage of some treatment agents is adjusted and controlled, so that the total hydrocarbon value is mostly controlled below 0.25% to ensure the authenticity and accuracy of logging data.
5 conclusion
An emulsion polymer which can be used as drilling fluid additive was synthesized by inverse microemulsion polymerization. It has good water solubility, viscosity increasing, machinability, water loss reduction and salt resistance. When the dosage of emulsion polymer is 0.4%, it can meet the basic requirements of drilling fluid performance. The pilot test results of emulsion polymerization show that the process is mature and stable, which can expand production.
Emulsion polymer is used in drilling fluid with positive charge. The field test of Dagu 1 well in No.2 structure of Dalaoba, Xinjiang shows that the drilling fluid coating has strong inhibition, good cuttings formation degree and sharp edge. Short tripping and tripping are extremely smooth, without any jamming phenomenon; The drilling fluid has strong anti-pollution ability and successfully passed through several sets of pure gypsum layers and high-pressure brine layers. The drilling diameter is very regular and the drilling quality is very good; The drilling fluid is clean, and the drill bit and centralizer are free of mud bags; The total hydrocarbon value and fluorescence level are well controlled, and the ideal application effect is achieved.
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