In Drilling, What Is the Rate of Penetration?

Reservoir protection technology during drilling refers to the technology to protect the reservoir by selecting appropriate drilling fluid and completion fluid technology to prevent reservoir pollution.

China also began to recognize the problem of reservoir damage in the 1950s. During the Daqing campaign in the 1960s, strict requirements were imposed on the drilling fluid density and fluid loss in drilling the formation; a small amount of work was performed in Changqing Oilfield in the 1970s; in the 1980s, especially through the "Seventh Five-Year" national key scientific and technological research and With the popularization and application of the "eighth five-year plan" and "ninth five-year plan", China has developed a series of relatively well-developed drilling technology to protect oil and gas layers.

The following main results have been achieved through tackling the problems: a set of indoor damage assessment devices, methods, and standards for reservoir damage at room temperature have been established, and the main damage mechanisms of these oil and gas reservoirs have been researched; the technology for evaluating reservoir damage mines has been improved and developed, Corresponding computer software; developed a new type of drilling and completion fluid treatment agent; developed a new type of drilling and completion fluid based on the potential damage characteristics of various types of oil and gas reservoirs; established a new formation pressure test method and improved and developed near-balanced drilling Technology, and carried out the practice of underbalanced pressure drilling; developed a wellbore structure suitable for protecting oil and gas layers, casing procedures and new methods of designing and selecting reservoir casings; developed a cementing slurry to prevent reservoir damage Additives, low-density cement slurry, supporting tools and cementing technology; developed a well completion method to protect oil and gas layers and a corresponding series of tools and equipment.

In general, except for some technologies that are limited by test equipment and equipment (such as reservoir damage evaluation technology that simulates formation conditions and actual working conditions, real-time monitoring while drilling, and joint testing technology, etc.), there are certain differences compared with foreign countries. Outside the gap, for projects that are less affected by equipment, such as conventional reservoir damage assessment and damage mechanism research technology, protection

In recent years, domestic and foreign scholars have conducted extensive and in-depth studies on the mechanism of reservoir damage, and have reached some recognized conclusions:

Solid phase particles in foreign fluids such as drilling fluids and completion fluids and original loose particles in the reservoir are migrated by external forces, directly blocking the pores and throats of rocks

The ultimate goal of drilling and completion is to drill the reservoir and form a channel for oil and gas flow to establish a good production relationship for the oil and gas well. Oil and gas layer damage will greatly affect the productivity of oil and gas wells. The main manifestation is the decrease of the permeability of oil and gas layers. During the drilling and completion process, the damage to the oil and gas layer is reduced by drilling and completion fluids, and the production of the oil and gas well is increased. The Bohai Oilfield has been developed for many years. With the continuous development of the reservoir, the physical properties and temperature and pressure systems of the main blocks of the oilfield have changed. Therefore, according to the characteristics of the reservoir, a performance optimization study of the drilling fluid reservoir protection site is performed to develop a suitable area. Implementation of technical measures for the protection of drilling fluid reservoirs on the development characteristics of block development wells.

In view of the technical characteristics of drilling and completion fluids at home and abroad, CBF film-forming plugging drilling fluid technology has been developed. CBF film-forming plugging drilling fluid technology is an organic combination of ultra-low permeability drilling fluid technology and broad-spectrum shielding temporary plugging protection oil and gas formation technology Fusion is based on the characteristics of the pore throat distribution of the reservoir, selecting the appropriate size of oil and gas layer protection additives, adjusting the solid phase particle size distribution of the drilling fluid to match the pore throat diameter distribution of the oil and gas layer, and achieving effective temporary plugging. At the same time, the characteristics of the film structure of the film-forming agent are used to block the pore throat of the oil layer and block the micropores between the rigid particles, thereby improving the blocking effect. Improve formation pressure capacity, expand safety density window, and achieve near-zero filtration protection of oil and gas layers.

Reservoir protection technology during drilling

1. Research and application of positive gel drilling fluid

MMH is the abbreviation of multilayer metal hydroxide, which is mainly composed of aluminum magnesium hydroxide. In the early 1990s, MMH was used abroad, and gradually adopted in China after 1993. MMH has been popularized and applied in Shengli Oilfield since 1994, and has formed a scale of about 600 to 800 wells per year. During the three years from 1996 to 1998, more than 2,000 wells were drilled with this technology, and the oil increase effect was obvious, and the added output value was several hundred million yuan. The potential value of MMH drilling fluid is mainly in the following aspects: good rheology and suspension performance; obvious ability to inhibit hydration of water-sensitive formations; and reducing the number of small size particles in drilling fluid.

The unique properties of the MMH system are particularly beneficial for oil layer protection: this drilling fluid maintains its solid state near the well wall, so the mechanical effect near the well wall is small, which is conducive to drilling a regular wellbore and maintaining small dynamics Dehydration. Field measurements proved that there is a layer of fluid static in the wellbore of 3/4 inch, and the fluid channel is near the drill pipe. The MMH system also has a strong inhibitory ability. With the increase of MMH concentration, the shale recovery rate increases. With the dilution of the base slurry, the range of shale recovery rate is small, but relatively speaking, at high MMH clay ratios, In the case, the shale recovery rate is high, indicating that MMH itself plays a role in inhibiting the hydration process.

In the past, the protection of oil and gas layers was mainly concerned with the physical properties of the producing layers and drilling fluid performance, but did not consider the influence of the electrical properties of the producing layers on the protection of the oil and gas layers. In 1997, a new mud treatment agent, Gaozheng Electric Black BPS, was developed, which has strong wall stability, good lubricating and anti-seizure properties, good oil layer protection, and excellent compatibility. The characteristics of vinyl BPS are that it has strong positive electricity, can be wetted by water, and has oil solubility, which can reduce the flow resistance when oil flows out. Therefore, BPS will play a more outstanding role in protecting oil and gas layers. Because it uses oil-soluble solutes and non-polar solvents for synthesis, its positive charge is twice as high as that of MMH positive charge glue, and the BPS potential of our indoor synthesis can reach 60 mv. This means that for the same amount of charged montmorillonite, a smaller amount of vinyl BPS can be used. The oil-soluble material used in the synthesis of BPS is a mechanical plugging agent, so BPS also has a certain anti-collapse effect. By using the treating agent with the base slurry, a highly inhibitive drilling fluid can be obtained. This drilling fluid can stabilize the borehole wall, carry cuttings, and suppress its dispersion, which is expected to reduce the cost of drilling fluid. ^[2]

2. Application of oil-based mud in water-sensitive reservoirs

Conventional oil-based mud, with diesel oil as the base liquid, high softening point slurry material, organic soil, caustic soda water, etc. as treatment agents. For indoor preparation, it needs to be heated to 70 80 . The finished oil slurry has high viscosity and cannot be used in winter. In view of the shortcomings of conventional oil-based muds, the following suggestions are proposed: low viscosity, good fluidity, less affected by temperature, and can be used in winter; the materials used are easily dispersed and dissolved in diesel and can be formulated without heating It is convenient for on-site construction. The API and HTHP filtration losses are low, the filter cake is thin, and the amount of solid phase intrusion into the oil layer is small to protect the oil and gas layer to the greatest extent. It has suitable performance parameters to ensure the well drilling construction.

In order to meet the above requirements, a lot of experimental work was carried out in the room. The oil-based mud developed at the end has stable performance and suitable rheological parameters, which can meet well-carrying wells and other requirements. The filtration loss is low and the filter cake is thin. Protect oil and gas layers. The performance parameters of the improved oil-based mud at 40 are as follows:

Density: 1. 80 g / cm3; Funnel viscosity: 50 80 mPa · s; Plastic viscosity: 20 40 mPa · s; API filtration loss: 1 2 mL; Static shear force: 5 8 Pa / 10 20 Pa; HTHP filtration loss: 5-7 mL.

The new oil-based mud formula is innovative in the following areas:

Use oil-based mud slurrying agent A instead of oil-based mud slurrying agent B. It can dissolve in diesel oil at normal temperature, creating conditions for realizing on-site slurry mixing.

Newly developed treatment agents such as oil-soluble suspending agent, flow pattern regulator, fluid loss reducer, SN-1 solid emulsifier, etc., are reasonably compatible to obtain a finished slurry with excellent performance.

The API and HTHP filter loss are low, the filter cake is thin, and the amount of solid phase intrusion into the oil layer is small, which can protect the oil and gas layer to the greatest extent.

The viscosity of the funnel of this formula is less affected by temperature, and it can be used normally in winter (-20 ° C).

3. Recyclable foam drilling and completion fluid technology

The characteristics of recyclable foam drilling fluid completion fluid are:

Low density, can be adjusted and recycled within the range of 0.6 to 0.99 g / cm ³ according to needs, and the original equipment of the well team can be used for construction;

After indoor evaluation, the core permeability recovery value was as high as 96.68%, so the system is effective in protecting oil and gas layers;

It can increase the drilling speed;

Little pollution to core and sensitive fluorescence display, which is conducive to discovering new oil and gas reservoirs. The recyclable foam drilling fluid completion fluid was successfully researched in 1995, and 2 wells were tested in the field; 5 wells were used in 1996; 1 well was used in 1997; and 12 wells were used in 1998. The number of wells is increasing year by year.

4. Laboratory test and field application research of polymerized drilling fluid

With the development of drilling technology and the pursuit of the benefits of exploration and development, drilling technology for complex wells such as directional wells, horizontal wells, branch wells with multiple bottoms, and cluster wells has become the direction of drilling development, and supporting oil-based drilling fluid applications Correspondingly, because oil-based drilling fluids can deal with complex formations, reduce the number of stuck drilling, which can save the total cost of drilling and reduce oil layer damage. However, the oil-based drilling fluids that used diesel as the base oil before could not meet the toxicity indicators proposed by the environmental protection department, especially the increasing number of offshore drilling operations. Restrictions are stricter. Since the 1980s, non-toxic (or low-toxic) oil-based drilling fluids have been developed abroad to meet ecological and environmental requirements. The biggest problem with this non-toxic drilling fluid is its high cost. It is said that its price is 3 to 6 times that of diesel in the international market. In addition, its low viscosity and the need for more thickeners increase its cost. , So it has not been promoted.

Adding one or more additives to water-based drilling fluids has the characteristics of oil-based drilling fluids, which has broad prospects. Nonionic alkoxy surfactants have been added to the formula, which has been used as a page since the mid 1950s. Rock inhibits the use of drilling fluids, and is accepted by people; water-based drilling fluids contain lower (1% to 5%) polyalcohols, which can improve the quality of wellbore stability, and were used as inhibitory shale drilling fluids in the 1960s. Field tests have proven that this system can improve drilling fluid characteristics in many ways.

With the deepening understanding of the importance of oil and gas layer protection, the research and application of oil and gas layer protection additives have received more and more attention. Polyalcohol has the functions of inhibiting mud shale hydration and expansion, improving drilling fluid lubricity, cleaning drilling tools, reducing filtration loss and protecting oil and gas layers, etc., and has the characteristics of low cost and no pollution to the environment. Beginning in the late 1980s abroad, polymer alcohols have been studied as the most potential oil and gas layer protection additives, and field applications have been made in the Gulf of Mexico and other areas, and good results have been achieved. Domestic studies on the role of polyalcohols in drilling fluids began in the mid-1990s, and field experiments in more than ten wells in the Tarim Oilfield and Shengli Oilfield have yielded satisfactory results. During the drilling process, it is too expensive to use polyalcohol mud in the whole well, so the focus of the work is on reservoir protection. Before drilling into the oil layer, the mud is modified to transform it into a polymer alcohol mud, to achieve the purpose of safely and quickly passing through the oil layer and reducing oil layer damage.

Polyalcoholic mud is modified by conventional water-based mud, and it is optimized by adding polyalcohol. This polymer alcohol has a sharp phase change process under the influence of temperature. It can be dissolved in water at the surface temperature, and it will precipitate from the water at the bottom of the well to form an emulsion. It will form a gel around the well wall to protect the oil layer and The function of stabilizing the wall of the well has good stability, lubricity and temperature resistance, and has low toxicity and does not pollute the environment. Laboratory experiments have proven that the mud can play a positive role in oil layer protection.

The mechanism of the role of polyalcohols in the protection of oil layers has the following aspects:

Suppression mechanism. Polyalcohol inhibits the hydration and expansion of clay in the formation and reduces the damage of clay minerals to the reservoir.

Cloud point behavior. When the polymer alcohol aqueous solution appears turbid, it can block formation pores and reduce the infiltration of mud filtrate to protect the oil and gas layer.

Hydrophobic effect. Polyalcohol adsorbs mud cake and formation pores to form a layer of hydrophobic oil film, which prevents mud filtrate from damage to the formation.

Form a complex. The polymer alcohol adsorbed on the clay surface interacts with potassium ions exchanged on the clay surface to form a complex, which can prevent direct contact between the clay and water, thereby preventing the hydration expansion of the clay and protecting the oil and gas layer.

There are many types of polyalcohols, and the molecular structure changes greatly. The mechanism of different polyalcohols in the protection of oil and gas layers is very different. At present, the research on the mechanism of polymer alcohols in the protection of oil and gas reservoirs has lagged behind the actual application, which will definitely affect the application effect and further popularize. The purpose is to deeply study the role of different types of polymer alcohols in the protection of oil and gas reservoirs, provide theoretical basis for the further development and promotion of the technology, and optimize the combination of polymer alcohols with different mechanisms of action in oil and gas layers. The best effect is achieved in protection, thus contributing to increasing reserves and production. Using this technology, it can replace the currently used oil layer protection materials. It has a good temporary blocking effect on other special reservoirs such as pore throat size and uneven distribution reservoirs, which are not very effective in shielding temporary blocking technology. Pollution is also an oil layer protection material that is well matched with synthetic-based mud, and has good economic, social, and environmental benefits.

5. Application of shielding temporary blocking technology

(1) Basic principles. Adding a certain amount of grading particles to the drilling and completion fluid, the particles penetrate the pore throat of the oil layer to cause blockage, which reduces the permeability of the oil layer. A shallow layer, i.e., an inner mud cake is formed near the surface of the exposed formation. Within minutes of opening the oil layer, A pollution zone with almost zero permeability is formed near the well wall near the reservoir. The depth of the contaminated zone into the oil layer is 1 to 10 cm, and the permeability of the contaminated zone is (0 to 1) × 10 ^-3 m ² . With the increase of the positive pressure difference, the shielding layer is denser, which will prevent the drilling fluid from continually contaminating the oil layer, thereby eliminating the damage to the oil layer due to the increase of soaking time, and also preventing the cementation slurry from contaminating the oil layer. . After completion of the well, the shield ring is lifted to restore the reservoir permeability, so it is also called temporary blockage, which can effectively protect the reservoir.

(2) Technical principles. The pressure difference between the drilling fluid column and the reservoir pores is a dynamic condition for forming the shield ring. The size of the solid particles of the drilling fluid is adjusted according to the size of the pore throat to match it. The bridge is bridged within 1 to 5 cm of the pore throat entrance and filled. Forming a shield ring to block the pore throat, and reducing its permeability to (0 1) × 10 ^-3 m ² , can effectively prevent the liquid phase from continuing to penetrate deep into the oil layer. The formation time of the effective shield ring is only related to the gradation of the solid phase particles in the completion fluid, the concentration of the solid particles in the bridge plug, the concentration of the filler particles, and the pressure difference. The reservoir type, clay content, and drilling fluid performance need not be considered. And system impact. The technology is low cost and easy to implement.

(3) The key of shielding temporary blocking technology-the selection of bridge plug particles and the determination of particle concentration. There are three kinds of solid phase particles in drilling fluids that protect the oil layer: a sufficient number of bridge plug particles that can stably bridge the pore throat of the oil layer; filler particles smaller than the bridging particles; highly dispersed particles that can withstand pressure differences and high temperatures Deformed particles, that is, denatured particles. The three kinds of particles act simultaneously to form the above-mentioned pollution zone. Three kinds of particles can be used in the shielding blocking technology to form a dense shielding ring. In practical applications, bridge plug particles generally use lightweight ultra-fine calcium carbonate, filled particles are small particles in drilling fluid, modified particles are selected from materials that soften at formation temperature, and sulfonated asphalt is generally used on land. Liquid materials have limited fluorescence, so oil-soluble resins can be used.

The characteristics of shielding blocking technology are:

Only the relationship between the fractures, pore throat radius, and solid phase particle gradation distributed in the drilling fluid is studied, regardless of the type of drilling fluid and other characteristics of the reservoir;

The increase in pressure difference is conducive to the temporary blocking technology. The larger the pressure difference, the better the effect;

The softening temperature of the deformed particles should match the reservoir temperature; The temporary blocking agent does not damage the original performance of the drilling fluid, and has some improving effects, such as reducing filtration loss.

The three kinds of particles exist in the drilling fluid at the same time, and the bridge plug particles are graded according to the 2/3 principle of the reservoir pore size. The average pore throat radius of the reservoir in Shengli Oilfield is generally less than 20 m, and the particle size measurement of drilling fluid shows that fine particles smaller than 5 m in the drilling fluid account for about 60% of the total solid phase, which can fully meet the needs of plugging. The diameter of the denatured particles is mostly in the range of 0.5 to 3 m. Generally, it is not necessary to control the particle size, only the concentration needs to be controlled, and the addition amount is not less than 1%.

Need to strictly control the particle diameter of bridge plug particles, the particle size of bridge plug particles is selected as follows:

(1) Basis for particle size selection of bridge plug particles. Calculate the reservoir pore distribution and the content of the total pore volume in each oil region, and calculate the percentage content of pores in the reservoir. Diameter distribution; list the pore diameter and its pore volume content, the particle size and content of bridge plug particles, and the particle size and content of drilling fluid.

(2) Determination of bridge plug particle concentration. After the particle size distribution of the bridge plug particles is determined, the calculation of the concentration of the reservoir and the amount of bridge plug particles to be plugged are calculated as follows.

Shielding temporary blocking technology is a high-quality, efficient and low-consumption oil and gas layer protection technology recognized by the petroleum science and technology community. Through systematic research on various cores, various temporary plugging agents, particle size and amount of particles, the formulation of drilling fluid and completion fluid for shielding temporary plugging technology was determined, and optimization continued. According to the physical properties of different oilfields and reservoirs (permeability, porosity, pore throat radius, mineral composition, sensitivity, etc.), technical measures for protecting oil and gas layers were proposed. The technology is easy to construct and will be widely used in large areas soon. The main oilfield for offshore development. ^[2]

Reservoir protection technology during drilling

CFR completion fluids are mainly composed of corrosion inhibition, anti-swelling, anti-emulsification, and sterilization agents. Its perforating fluid is mainly composed of chelating acids, mutual solvents, corrosion inhibition, anti-swelling, anti-emulsification, sterilization and other agents. Its mechanism of action is mainly:

First: the corrosion inhibitor forms a good film layer on the metal surface, which isolates or reduces the contact area between the acid liquid and the metal to inhibit corrosion; at the same time, the corrosion inhibitor has good compatibility with the completion fluid.

Second: The iron ion chelating agent can effectively prevent the formation of iron hydroxide precipitation in the formation due to the decrease of PH value, which can cause formation blockage damage. It stabilizes Fe3 + ions in the formation through the dual effects of reduction and chelation, and reduces the formation blockage due to precipitation. Seam hole.

Third: The polymer clay stabilizer can form a tight bond with the clay, and it is not easy to dissociate in water to form a diffusion double layer that makes the clay swell easily, thereby effectively preventing the clay from expanding and reducing the water content of the shale. The formation, expansion and dispersion are beneficial to the stability of sensitive sandstone clay minerals.

Fourth: Waterproof lock emulsifier has low surface tension and ultra-low oil-water interface tension, which can effectively increase the same flow zone of oil and water, change the percolation characteristics of fluids in low-permeability reservoirs, increase the initial pressure gradient of injected water, and reduce crude oil seepage The initial pressure gradient makes the oil-water fluidity closer, reduces the "stuck" phenomenon of oil, and reduces the Jiamin effect.

Fifth: Mutual solvents are a class of substances that have a certain solubility in both oil and water, and can be mixed with both oil and water. After entering the formation, they preferentially adsorb on the surface of sand grains and clay, which not only makes the particles and insoluble matter wet with water, but also makes the formation water-wet, which improves the permeability of the formation. Maintenance principles during on-site construction:

1. Ensure that the early working cycle system is clean and free of pollution, and the wellbore is clean.

2. Completion operations choose compatible completion fluids to reduce formation damage.

3 When opening the oil layer, make sure to perforate with negative pressure to reduce the contact of various liquids with the formation.

4 Ensure that the particle size of the liquid in contact with the formation matches the meniscus size. (2 microns to 5 microns)

5. Ensure turbidity NTU 30 to reduce the precipitation and scaling of organic and inorganic substances caused by physical-chemical-thermodynamic effects; reduce various sensitive reactions such as water, alkali, acid, solid phase and cement.

6. Control reasonable production pressure difference and prevent pollution from formation sand production and particle migration.

7. Maintain performance indicators of completion fluids to ensure smooth operations.

8. Maintain the anti-discharge and deblocking properties of various liquids, improve the permeability recovery rate of oil layers, increase production capacity, and improve oil recovery. ^[1]