# Damage of Green Synthetic Cement Slurry to Clastic Rock Reservoir

Authors: Meng Xu; Xin Tan; Libo Yang; Hanlie Cheng; David Cofell
Journal: Journal of Chemistry
 (2023)

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## Abstract

Green synthesis and metal oxide composites have attracted much attention from researchers of industry and academia. As a typical application of green synthesis and metal oxide composites, the protection of oil and gas reservoirs is related to various links such as exploration, drilling, completion, and development. It is a complex and systematic project, which directly affects whether the oil and gas fields can be discovered, evaluated, and efficiently developed in time, and it is also related to the development of oil and gas fields recovery rate. As the most critical part of oil and gas well construction, the cementing process mainly pays attention to the safe pumping of the cement slurry and the long-term effective interlayer isolation capability of the cement sheath. Less attention is paid to the reservoir protection during the cementing process. The high-pressure difference between the annulus and the formation, the high fluid loss, and the high solids content of the cementing slurry during the cementing process have also become major challenges. In order to solve this problem, this study takes a typical clastic rock block in an oilfield in western China as the research object and carries out a geological survey of fracture development, pressure deficit, and cement slurry permeability leakage in the reservoir. The reservoir physical properties, clay mineral characteristics, and formation water quality of rock reservoirs are analyzed. The influence of cement slurry filtrate and solid phase particles on reservoir clay expansion rate and permeability was tested by core porosity and permeability tester. XRD and SEM techniques were used to analyze the damage mechanism of cement slurry filtrate and solid phase particles to the reservoir. The research results show that the average porosity of the clastic rock reservoir in the study area is 15%, the permeability is high, the average pore size of the reservoir is between 37 and 56μm, the microfractures are developed in the reservoir section, and the porosity and permeability conditions are good; high-valent cations and inorganic ions in the filtrate generate inorganic scales such as CaCO3 and Mg(OH)2 and cross-link with dissolved polymers to form flocculation substances, which cause the filtrate to damage the reservoir, and at the same time, the cement particles in the pore throats in the near wellbore zone are lost along with the leakage. Furthermore, hydration, tightly bonding the inert admixture and the clastic rock formation, forms a tight sealing layer, which reduces the permeability of the reservoir sharply; the expansive clay particles in the reservoir absorb the moisture of the cement slurry filtrate and expand. The volume of the particles increases, and the porous formation containing expansive clay minerals absorbs moisture and causes internal expansion, and the volume expansion rate can reach 9%, which eventually causes the porosity and permeability of the reservoir to decrease, resulting in reservoir damage and solid phase in the cement slurry. The damage of particles to the reservoir is mainly due to the blockage of the reservoir pore throats and the hydration and consolidation of cement particles inside the reservoir caused by the external admixtures in the cement slurry that do not participate in the hydration reaction. The solid phase particles form a filter cake on the surface of the reservoir core and cannot enter the reservoir, but under the condition of porous formation leakage, the solid phase particles with a particle size of 1–10 μm in the cement slurry will directly penetrate into the reservoir rock resulting in shallow plugging in the reservoir near the wellbore. The research results provide theoretical data support for the research on low-damage cementing slurry technology in clastic rock reservoirs. The work provides an important application guidance to green synthesis and metal oxide composites.


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## Body

## 1. Introduction

It is important to investigate green synthesis and metal oxide composites. As a typical application of green synthesis and metal oxide composites, reservoir damage directly affects the loss of oil and gas resources, increases production costs, and is more likely to cause complex and serious problems in the production process of oil and gas wells [1–3]. Before the exploitation of oil and gas reservoirs, the rock, mineral components, and fluids contained in the oil and gas reservoirs are in a state of equilibrium. However, this equilibrium state is likely to be broken during the construction of oil and gas wells and subsequent production, resulting in the formation of reservoirs, and damage occurs. Reservoir damage is mainly manifested as a linear drop in the absolute or relative permeability of the reservoir [4–7]. The protection of oil and gas reservoirs is related to various links such as exploration, drilling, completion, and development. It is a complex and systematic project, which directly affects whether the oil and gas fields can be discovered, evaluated, and efficiently developed in time, and it is also related to the development of oil and gas fields recovery rate [8–11]. As the most critical part of oil and gas well construction, the cementing process mainly pays attention to the safe pumping of the cement slurry and the long-term effective interlayer isolation capability of the cement sheath. Less attention is paid to the reservoir protection during the cementing process. The high-pressure difference between the annulus and the formation, the high fluid loss, and high solids content of the cementing slurry during the cementing process have also become major challenges [12–15].Scholars at home and abroad have carried out research on the damage mechanism of oil and gas reservoirs in the cementing process and have achieved certain research results. Some researchers have carried out the internal relationship between the quality of the mud cake of the drilling fluid and the degree of damage to the reservoir by the cement slurry [10, 16–18]. The formation of better quality internal and external mud cakes can effectively prevent the damage of drilling fluid and cement slurry to oil and gas reservoirs, so as to achieve the purpose of protecting reservoirs. Some researchers took the low-porosity and low-permeability reservoirs in the Songnan area as the research object, studied the damage degree of the cement slurry to the reservoir, established a damage model, and checked that the intrusion depth of cement slurry filtrate in this area is generally within 5 cm [12, 19–21]. The damage to the reservoir is small, and this damage can be canceled by perforating. Some researchers have carried out research on the damage degree of cement slurry filtrate to the reservoir, showing that the cement slurry filtrate will cause serious reservoir damage [22–25]. The combination of fine cement particles blocks the pore throats of the reservoir, resulting in a decrease in the permeability of the reservoir. Therefore, reducing the fluid loss of the cement slurry can effectively reduce the damage to the reservoir during the cementing process. Some researchers have studied the effect of different cement admixtures on the ionic composition of cement slurry filtrate. When the types of admixtures are different, the ionic content in the filtrate will cause different damage to the reservoir, mainly because long-chain admixtures can cause harmful effects. The increase of the ion concentration is not conducive to the protection of the reservoir, and the retarder can effectively reduce the harmful ion concentration of the filtrate to achieve the purpose of protecting the reservoir. Some researchers have studied the compatibility of cement slurry filtrate and formation water, the influence of crystals and sediments on reservoir conductivity through experiments, and explored the damage mechanism of the cement slurry to the reservoir and the impermeability and low water loss cement. Research on reservoir protection by slurry: Some researchers have evaluated the damage caused by the cement slurry filtrate and its precipitates to the reservoir through experiments because the reaction of the cement slurry filtrate and the solid phase particles in the filtrate with the reservoir begins immediately after the cement slurry is in contact with the reservoir, although the cement slurry is in contact with the reservoir. The slurry filtrate has a wide range of filtration loss, but the insoluble matter or precipitation reaction reacts rapidly in the area where the filtrate penetrates, resulting in the precipitation of high-capacity and low-molecular-weight hydration products near the wellbore. Changes in the volume of the solid phase depend on the mass balance (material balance). Some researchers took clastic rock reservoirs as the research object and carried out research on the damage of cementing cement slurry to clastic rock reservoirs in a medium-porous and medium-permeable sandstone reservoir in an oilfield. The lithological characteristics, physical characteristics, pore throat characteristics, and temperature and pressure characteristics of the clastic rock reservoir are analyzed, and the factors that may cause potential damage to the reservoir are analyzed from the aspects of clay mineral content, formation fluid properties, and cementing slurry characteristics, and the study area is obtained. Potential damage factors for blocks include sensitivity damage, inorganic scale precipitation damage, and cement slurry solid phase particle blockage damage.The most critical part of the development and construction of oil and gas wells: During the cementing process, the high-pressure difference between the annulus and the formation, the high fluid loss, and the high solids content of the cementing slurry cause serious damage to the reservoir. Damage has also become a major problem. In this paper, taking a typical clastic rock reservoir in an oilfield in western China as the research object, the geological investigation of fracture development, pressure deficit, and cement slurry permeability loss during the cementing process was carried out in the reservoir, and the reservoir of clastic rock reservoir was studied. Analysis of physical properties, clay mineral characteristics, and formation water quality. The influence of cement slurry filtrate and solid phase particles on the expansion rate and permeability of reservoir clay was tested by using a core porosity and permeability tester. The damage mechanism of solid phase particles to the reservoir is of great significance to the development of low-damage cementing slurry technology for clastic rock reservoirs.


## 2. Geological Features

### 2.1. Geological Overview Based Green Synthesis

In this paper, the typical clastic rock blockD of an oilfield in western my country is selected as the research background, and the reservoir characteristics and cementing overview of the block are carried out. The oil and gas-bearing scrotal rock reservoirs in the study area are mainly distributed in the Paleogene Kumugelimu Group, the Cretaceous Bashkirqike Formation, and the Brazil Reorganization, among which the Paleogene Kumugelimu Group lithology mainly includes fine sandstone, argillaceous siltstone, glutenite, and silty mudstone; Cretaceous Bashkirqike Formation lithology mainly includes fine sandstone, argillaceous siltstone, siltstone, silty mudstone, and mudstone; the reorganized lithology in Brazil is mainly mudstone, silty mudstone, fine sandstone, and argillaceous siltstone. On the whole, the stratum is characterized by “mud above and below sand.” Table 1 shows the temperature of the reservoir section in the study area. It can be seen from Table 1 that the temperature gradient of the reservoir is 1.98∼2.11°C/100 m, the burial depth is in the range of 4000∼5000 m, and the temperature is between 100 and 200°C.Table 1
Reservoir section temperature in the study area with green synthesis and metal oxide composites.
BlockGeothermal gradientClastic reservoir temperatureD1.98∼2.11°C/100 m100∼200°CTable2 gives the pressure measurement coefficients of the reservoir sections in the study area. It can be seen from Table 2 that after years of oil and gas exploitation, the clastic rock reservoir section has appeared obvious pressure deficit, and the pressure coefficient has generally dropped below 1. At the same time, due to the pressure deficit, the pressure difference during cementing is relatively low, high, or even as high as 15∼25 MPa.Table 2
Pressure measurement coefficients of reservoir sections in the study area.
HashtagHorizonMid-depth of gas layer (m)Formation pressure (MPa)Pressure coefficientD-02E514056.51.13D-08E503250.11.01D-15E + K494248.60.92D-24E + K483145.20.89D-32E526141.60.81Through geological survey and core observation, the clastic rock reservoir in the study area is loose due to the low pressure of the overlying stratum, and the rock cementation in the upper part of the reservoir is loose, mainly in the pore-type stratum, and the lower reservoir is due to the pressure of the overlying stratum. Larger, the rock cementation is tight, but under the action of geological tectonic deformation and tectonic stress, rupture has occurred, forming shrinkage fractures or structural fractures, and the permeability of the reservoir is good. Through the study of drilling cores in this block, it is found that 8 of the 45 cores in the reservoir section of the study area have structural fractures or shrinkage fractures, and the fractures account for as high as 18%, of which the largest fracture width is 0.4 mm.The width is large, and under the action of high-pressure difference in cementing, the cement slurry can completely enter the reservoir through the fracture; at the same time, the average porosity of the core reaches 15%, the average permeability is 118.6 mD, and the pore size distribution is 37–56μm. The pore types are mainly intergranular dissolved pores and intragranular dissolved pores. The average clay mineral content in this area is between 2% and 11%, and the clay mineral type is mainly illite, accounting for about 50% of the clay content. %∼80%, the ratio is 25%∼35%, the ratio of which is 25%∼35%. The salinity of formation water is as high as 1.84 × 105 mgL, and the concentration of Ca2+ in the formation water is higher, and it also contains a higher concentration of Mg2+ and SO42−.


### 2.2. Overview of Cementing Based Green Synthesis

The cementing in this block mainly adopts the 5-layer casing structure of 20” × 133/8” × 7” × 5”, the liner cementing process, and the one-time cementing scheme. A survey was carried out, and the LD cement slurry system was mainly used, and the formula of each well was not much different. In this paper, the liner cementing slurry of a certain well is randomly selected to carry out experimental research. Table3 gives the cement slurry formulation. For fractured shoulder rock reservoir, polysulfonate antisloughing drilling fluid system (%), temporary plugging agent (24%), caustic soda (0.4%), and weighting agent are mainly used. In cementing, a microstrength isolation fluid system is used, and the main ingredients are weighting agent (50%), retarder (3%), dispersant (3%), suspending agent (1%), defoamer (0.5%), water.Table 3
Cement slurry formula with green synthesis and metal oxide composites.
TypeG classCementSilicon powderWater retarderDispersantåwater loss reducerDefoamerAddition (%)10036342.51.35.20.In the cementing process, the cementing conditions, reservoir characteristics, and the damage of cement slurry to the reservoir are highly correlated. When the reservoir does not leak, it is necessary to consider the damage to the reservoir caused by the cement slurry of the mud cake inside and outside the drilling fluid. When leakage occurs in the reservoir, the type of leakage is related to the characteristics of the reservoir. In the upper part of the scribbled rock reservoir, the reservoir type is mainly pore-type strata, and the conditions of porosity and permeability are good. The bottom of the clastic rock reservoir is mainly a pore-fracture type formation, and fracture leakage often occurs.The development of fractures in the reservoir provides space for oil and gas accumulation, provides channels for natural oil and gas migration, and plays an extremely important role in the seepage of oil and gas in the reservoir. For pore-fractured formations, permeability leakage may occur during cementing under the action of high-pressure difference, cement slurry easily flows into the fractures, and hydration occurs and finally solidifies and blocks microfractures in the reservoir, which will cause damage to oil and gas production in the later stage more serious impact.


### 2.3. Test Conditions Based Green Synthesis

The test material in this paper is the core of typical clastic rock blockD in an oilfield in the west. The ingredients used for cementing cement are simulated formation water, G-grade cement, mutual force silica fume, coagulant, fluid loss reducer, dispersant, retarder, and defoamer. The test mainly used a constant speed stirrer, high temperature, and high-pressure water loss instrument: DKS-2 core porosity and permeability tester, DX-2000 X-ray diffractometer, TM-1000 electron scanning microscope, and CPD-II high-temperature and high-pressure dilatometer.In order to truly simulate the damage of the cement slurry to the clastic rock reservoir under this working condition, artificial fractures were made on the reservoir cores, and the dynamic experiments of the cement slurry were carried out using the fractured cores. Figure1 shows the dynamic experimental flow of the cement slurry. In the test, the cores contaminated with cement slurry were placed in a high-temperature and high-pressure curing kettle for curing. The temperature during curing was set to 120°C, the curing pressure was 75 MPa, and the curing time was taken out after 24 hours. The acid solution with a concentration of 15% was used to simulate acid dissolution. Its permeability recovery value is plugged and calculated. For pore-fractured formations, when the cement slurry leaks out, it causes serious damage to the reservoir, the fractures in the core are filled with cement, and the permeability damage rate exceeds 80%. Due to the consolidation ability of cement slurry, the acid solubility of cement stone after curing with conventional cement slurry is low, and the permeability recovery value after plugging by acid dissolution is less than 50%. The reservoir damage caused by cement slurry consolidation still cannot be effectively relieved.Figure 1
Dynamic experiment flow of cement slurry with green synthesis and metal oxide composites.


## 2.1. Geological Overview Based Green Synthesis

In this paper, the typical clastic rock blockD of an oilfield in western my country is selected as the research background, and the reservoir characteristics and cementing overview of the block are carried out. The oil and gas-bearing scrotal rock reservoirs in the study area are mainly distributed in the Paleogene Kumugelimu Group, the Cretaceous Bashkirqike Formation, and the Brazil Reorganization, among which the Paleogene Kumugelimu Group lithology mainly includes fine sandstone, argillaceous siltstone, glutenite, and silty mudstone; Cretaceous Bashkirqike Formation lithology mainly includes fine sandstone, argillaceous siltstone, siltstone, silty mudstone, and mudstone; the reorganized lithology in Brazil is mainly mudstone, silty mudstone, fine sandstone, and argillaceous siltstone. On the whole, the stratum is characterized by “mud above and below sand.” Table 1 shows the temperature of the reservoir section in the study area. It can be seen from Table 1 that the temperature gradient of the reservoir is 1.98∼2.11°C/100 m, the burial depth is in the range of 4000∼5000 m, and the temperature is between 100 and 200°C.Table 1
Reservoir section temperature in the study area with green synthesis and metal oxide composites.
BlockGeothermal gradientClastic reservoir temperatureD1.98∼2.11°C/100 m100∼200°CTable2 gives the pressure measurement coefficients of the reservoir sections in the study area. It can be seen from Table 2 that after years of oil and gas exploitation, the clastic rock reservoir section has appeared obvious pressure deficit, and the pressure coefficient has generally dropped below 1. At the same time, due to the pressure deficit, the pressure difference during cementing is relatively low, high, or even as high as 15∼25 MPa.Table 2
Pressure measurement coefficients of reservoir sections in the study area.
HashtagHorizonMid-depth of gas layer (m)Formation pressure (MPa)Pressure coefficientD-02E514056.51.13D-08E503250.11.01D-15E + K494248.60.92D-24E + K483145.20.89D-32E526141.60.81Through geological survey and core observation, the clastic rock reservoir in the study area is loose due to the low pressure of the overlying stratum, and the rock cementation in the upper part of the reservoir is loose, mainly in the pore-type stratum, and the lower reservoir is due to the pressure of the overlying stratum. Larger, the rock cementation is tight, but under the action of geological tectonic deformation and tectonic stress, rupture has occurred, forming shrinkage fractures or structural fractures, and the permeability of the reservoir is good. Through the study of drilling cores in this block, it is found that 8 of the 45 cores in the reservoir section of the study area have structural fractures or shrinkage fractures, and the fractures account for as high as 18%, of which the largest fracture width is 0.4 mm.The width is large, and under the action of high-pressure difference in cementing, the cement slurry can completely enter the reservoir through the fracture; at the same time, the average porosity of the core reaches 15%, the average permeability is 118.6 mD, and the pore size distribution is 37–56μm. The pore types are mainly intergranular dissolved pores and intragranular dissolved pores. The average clay mineral content in this area is between 2% and 11%, and the clay mineral type is mainly illite, accounting for about 50% of the clay content. %∼80%, the ratio is 25%∼35%, the ratio of which is 25%∼35%. The salinity of formation water is as high as 1.84 × 105 mgL, and the concentration of Ca2+ in the formation water is higher, and it also contains a higher concentration of Mg2+ and SO42−.


## 2.2. Overview of Cementing Based Green Synthesis

The cementing in this block mainly adopts the 5-layer casing structure of 20” × 133/8” × 7” × 5”, the liner cementing process, and the one-time cementing scheme. A survey was carried out, and the LD cement slurry system was mainly used, and the formula of each well was not much different. In this paper, the liner cementing slurry of a certain well is randomly selected to carry out experimental research. Table3 gives the cement slurry formulation. For fractured shoulder rock reservoir, polysulfonate antisloughing drilling fluid system (%), temporary plugging agent (24%), caustic soda (0.4%), and weighting agent are mainly used. In cementing, a microstrength isolation fluid system is used, and the main ingredients are weighting agent (50%), retarder (3%), dispersant (3%), suspending agent (1%), defoamer (0.5%), water.Table 3
Cement slurry formula with green synthesis and metal oxide composites.
TypeG classCementSilicon powderWater retarderDispersantåwater loss reducerDefoamerAddition (%)10036342.51.35.20.In the cementing process, the cementing conditions, reservoir characteristics, and the damage of cement slurry to the reservoir are highly correlated. When the reservoir does not leak, it is necessary to consider the damage to the reservoir caused by the cement slurry of the mud cake inside and outside the drilling fluid. When leakage occurs in the reservoir, the type of leakage is related to the characteristics of the reservoir. In the upper part of the scribbled rock reservoir, the reservoir type is mainly pore-type strata, and the conditions of porosity and permeability are good. The bottom of the clastic rock reservoir is mainly a pore-fracture type formation, and fracture leakage often occurs.The development of fractures in the reservoir provides space for oil and gas accumulation, provides channels for natural oil and gas migration, and plays an extremely important role in the seepage of oil and gas in the reservoir. For pore-fractured formations, permeability leakage may occur during cementing under the action of high-pressure difference, cement slurry easily flows into the fractures, and hydration occurs and finally solidifies and blocks microfractures in the reservoir, which will cause damage to oil and gas production in the later stage more serious impact.


## 2.3. Test Conditions Based Green Synthesis

The test material in this paper is the core of typical clastic rock blockD in an oilfield in the west. The ingredients used for cementing cement are simulated formation water, G-grade cement, mutual force silica fume, coagulant, fluid loss reducer, dispersant, retarder, and defoamer. The test mainly used a constant speed stirrer, high temperature, and high-pressure water loss instrument: DKS-2 core porosity and permeability tester, DX-2000 X-ray diffractometer, TM-1000 electron scanning microscope, and CPD-II high-temperature and high-pressure dilatometer.In order to truly simulate the damage of the cement slurry to the clastic rock reservoir under this working condition, artificial fractures were made on the reservoir cores, and the dynamic experiments of the cement slurry were carried out using the fractured cores. Figure1 shows the dynamic experimental flow of the cement slurry. In the test, the cores contaminated with cement slurry were placed in a high-temperature and high-pressure curing kettle for curing. The temperature during curing was set to 120°C, the curing pressure was 75 MPa, and the curing time was taken out after 24 hours. The acid solution with a concentration of 15% was used to simulate acid dissolution. Its permeability recovery value is plugged and calculated. For pore-fractured formations, when the cement slurry leaks out, it causes serious damage to the reservoir, the fractures in the core are filled with cement, and the permeability damage rate exceeds 80%. Due to the consolidation ability of cement slurry, the acid solubility of cement stone after curing with conventional cement slurry is low, and the permeability recovery value after plugging by acid dissolution is less than 50%. The reservoir damage caused by cement slurry consolidation still cannot be effectively relieved.Figure 1
Dynamic experiment flow of cement slurry with green synthesis and metal oxide composites.


## 3. Damage of Cement Slurry to Clastic Rock Reservoir

### 3.1. Damage to Reservoir by Cement Slurry Filtrate Based Green Synthesis

In this paper, the cement slurry filtrate and formation water are mixed and placed in a wide-mouth bottle according to different volume ratios and then cured in a water bath. The curing temperature is 90°C and the curing time is 24 hours. After that, the scaling phenomenon occurs, and the scaling form is granular. Crystallized and flocculated precipitates. The flocculated substances generated were analyzed by infrared spectroscopy, and it was obvious that the flocculent scale was obviously organic, indicating that the cement slurry admixture contained high-molecular polymers. Under the action of high-valent cations in the formation of water, the polymer molecules were a cross-linked phenomenon, resulting in flocculationlike scaling. These flocculated scales are more likely to block the critical parts of the reservoir pore throat isosmotic flow. Table4 and Figure 2 show the scaling amount of different ratios of cement slurry filtrate and formation water. It can be seen from Table 4 and Figure 2 that with the increase of the ratio of cement slurry filtrate and formation water, the scaling amount first increases and then decreases. When the volume ratio of the filtrate to formation water is 3 : 2, the amount of scaling is the largest.Table 4
Compatibility test results of cement slurry filtrate and formation water.
Serial numberCement slurry filtrate volume (ml)Formation water volume (ml)Scaling amount (g)120800.07240600.31360400.68480200.21Figure 2
Scaling amount of different ratios of cement slurry filtrate and formation water with green synthesis and metal oxide composites.CPD-II type high temperature and high-pressure dilatometer was used to test the volume expansion rate of clastic rock reservoir cores under the action of cement slurry filtrate. Figure3 shows the test results of the reservoir rock expansion rate. It can be seen from Figure 3 that with the extension of time, under the action of the cement slurry filtrate, the reservoir core will undergo obvious hydration expansion, and the expansion rate of the filtrate and the reservoir rock will increase rapidly in the first 2 hours after contact; the final volume expand Rate will reach 8%.Figure 3
Reservoir rock expansion rate test with green synthesis and metal oxide composites.The core-flooding device was used to carry out the damage experiment of the cement slurry filtrate on the core. Table5 shows the influence of the cement slurry filtrate on the core permeability. It can be seen from Table 5 that the cement slurry filtrate has a great influence on the core permeability up to 92%. In the test, the porosity and permeability of reservoir core before filtrate damage are good, and a large amount of flocculent scaling appeared at the pore throat after the damage, which caused the blockage of the pore throat.Table 5
Experiment on the effect of cement slurry filtrate on core permeability.
Rock sample numberPermeability (mD)D (%)KaKoKd1410.250.07812754.030.598631084.270.418941355.840.5692Through the core damage test of cement slurry filtrate, the main reason is that during the hydration process and the crystallization of inorganic substances damages the cement slurry and produces many inorganic ions. In a higherpH environment, the inorganic ions generated by hydration will exist in the cement in a saturated state. During cementing construction, after the filtrate enters the reservoir, the original ion balance is destroyed, resulting in the precipitation of CaCO3, Mg(OH)2, and the like. The crystals were separated and obtained by suction filtration, and analyzed by X-ray diffractometer, which proved that Mg(OH)2 and CaCO3 existed in the crystals. The cement slurry filtrate is strongly alkaline. Once the filtrate enters the reservoir, it will affect the chargeability of the clay mineral lattice surface of the reservoir. The amount of OH− adsorption on the clay surface will increase, and the electrostatic repulsion between the clay mineral crystal layers will increase. For the reservoir, clay minerals are more likely to swell and disperse.


### 3.2. Analysis of the Damage Mechanism of Cement Slurry Solid Phase Particles to the Reservoir Based Green Synthesis

In cementing construction, with the filtration of cement slurry, cement particles and external admixtures will enter the reservoir together with the filtrate, undergo a hydration reaction, and finally consolidate inside the reservoir, while the external admixture directly blocks the reservoir. Layer pore throats cause damage. For cores that have not been damaged by cement slurry, pore throats are more developed. When the cement slurry damages the reservoir, the amorphous cementitious components contained in the pore throats fill the rock pores and fractures and contain spherical particles, indicating that the cement slurry does not participate in the hydration reaction of external admixtures.Through the analysis of the particle size distribution and cumulative particle size distribution of the cement slurry solid phase particles, the particle size of the solid phase particles in the cement slurry is between 1 and 1000μm, and the overall particle size is relatively large. The volume of phase particles accounts for the largest proportion, while the smaller particles with a particle size of 1–10 μm account for about 15% of the total volume of the solid phase.According to the plugging criteria of Barkman and Abrams (Table6), it can be seen that when the pore size of the reservoir rock is less than 3 times the particle size of the solid phase, the solid phase particles will bridge the surface of the permeable layer to form a filter cake; When the rock pore size is less than 10 times the solid particle size, the solid particles enter the reservoir near the wellbore to form shallow plugging; if the rock pore size is greater than 10 times the solid particle size, the solid particles enter the deep part of the permeable layer, increasing the depth of plugging.Table 6
Barkman and Abrams blocking criteria.
Particle size rangeDamage resultThe rock pore size is less than 3 times the solid phase particle sizeSurface bridging to form a filter cake3 times the particle size of the solid phase < rock pore diameter < 10 times the particle size of the solid phaseShallow plugging near wellboreIf the rock pore size is greater than 10 times the solid phase particle sizeDeep blockageAccording to the pore size test results of clastic rock reservoirs under different working conditions, the particle size distribution, and cumulative particle size distribution of cement slurry solid phase, it can be concluded that under the condition of no leakage, the original pore size of the reservoir is 0.1∼100μm. Among them, the pore size in the range of 1–10 μm accounts for the largest proportion, and the pore size is similar to the smaller particle size in the cement slurry. Therefore, under this working condition, the solid phase particles of the cement slurry cannot enter the reservoir. As a result, a filter cake will be formed on the surface of the reservoir core; under the leakage condition, due to the loss of the protection of the mud cake in the drilling fluid, the solid phase particles of the cement slurry will directly contact the reservoir rock. The proportion between ∼50 μm is the largest, and the part of the solid particles in the cement slurry with a solid particle size of 1 to 10 μm will enter the reservoir and form shallow plugging in the reservoir near the wellbore.


## 3.1. Damage to Reservoir by Cement Slurry Filtrate Based Green Synthesis

In this paper, the cement slurry filtrate and formation water are mixed and placed in a wide-mouth bottle according to different volume ratios and then cured in a water bath. The curing temperature is 90°C and the curing time is 24 hours. After that, the scaling phenomenon occurs, and the scaling form is granular. Crystallized and flocculated precipitates. The flocculated substances generated were analyzed by infrared spectroscopy, and it was obvious that the flocculent scale was obviously organic, indicating that the cement slurry admixture contained high-molecular polymers. Under the action of high-valent cations in the formation of water, the polymer molecules were a cross-linked phenomenon, resulting in flocculationlike scaling. These flocculated scales are more likely to block the critical parts of the reservoir pore throat isosmotic flow. Table4 and Figure 2 show the scaling amount of different ratios of cement slurry filtrate and formation water. It can be seen from Table 4 and Figure 2 that with the increase of the ratio of cement slurry filtrate and formation water, the scaling amount first increases and then decreases. When the volume ratio of the filtrate to formation water is 3 : 2, the amount of scaling is the largest.Table 4
Compatibility test results of cement slurry filtrate and formation water.
Serial numberCement slurry filtrate volume (ml)Formation water volume (ml)Scaling amount (g)120800.07240600.31360400.68480200.21Figure 2
Scaling amount of different ratios of cement slurry filtrate and formation water with green synthesis and metal oxide composites.CPD-II type high temperature and high-pressure dilatometer was used to test the volume expansion rate of clastic rock reservoir cores under the action of cement slurry filtrate. Figure3 shows the test results of the reservoir rock expansion rate. It can be seen from Figure 3 that with the extension of time, under the action of the cement slurry filtrate, the reservoir core will undergo obvious hydration expansion, and the expansion rate of the filtrate and the reservoir rock will increase rapidly in the first 2 hours after contact; the final volume expand Rate will reach 8%.Figure 3
Reservoir rock expansion rate test with green synthesis and metal oxide composites.The core-flooding device was used to carry out the damage experiment of the cement slurry filtrate on the core. Table5 shows the influence of the cement slurry filtrate on the core permeability. It can be seen from Table 5 that the cement slurry filtrate has a great influence on the core permeability up to 92%. In the test, the porosity and permeability of reservoir core before filtrate damage are good, and a large amount of flocculent scaling appeared at the pore throat after the damage, which caused the blockage of the pore throat.Table 5
Experiment on the effect of cement slurry filtrate on core permeability.
Rock sample numberPermeability (mD)D (%)KaKoKd1410.250.07812754.030.598631084.270.418941355.840.5692Through the core damage test of cement slurry filtrate, the main reason is that during the hydration process and the crystallization of inorganic substances damages the cement slurry and produces many inorganic ions. In a higherpH environment, the inorganic ions generated by hydration will exist in the cement in a saturated state. During cementing construction, after the filtrate enters the reservoir, the original ion balance is destroyed, resulting in the precipitation of CaCO3, Mg(OH)2, and the like. The crystals were separated and obtained by suction filtration, and analyzed by X-ray diffractometer, which proved that Mg(OH)2 and CaCO3 existed in the crystals. The cement slurry filtrate is strongly alkaline. Once the filtrate enters the reservoir, it will affect the chargeability of the clay mineral lattice surface of the reservoir. The amount of OH− adsorption on the clay surface will increase, and the electrostatic repulsion between the clay mineral crystal layers will increase. For the reservoir, clay minerals are more likely to swell and disperse.


## 3.2. Analysis of the Damage Mechanism of Cement Slurry Solid Phase Particles to the Reservoir Based Green Synthesis

In cementing construction, with the filtration of cement slurry, cement particles and external admixtures will enter the reservoir together with the filtrate, undergo a hydration reaction, and finally consolidate inside the reservoir, while the external admixture directly blocks the reservoir. Layer pore throats cause damage. For cores that have not been damaged by cement slurry, pore throats are more developed. When the cement slurry damages the reservoir, the amorphous cementitious components contained in the pore throats fill the rock pores and fractures and contain spherical particles, indicating that the cement slurry does not participate in the hydration reaction of external admixtures.Through the analysis of the particle size distribution and cumulative particle size distribution of the cement slurry solid phase particles, the particle size of the solid phase particles in the cement slurry is between 1 and 1000μm, and the overall particle size is relatively large. The volume of phase particles accounts for the largest proportion, while the smaller particles with a particle size of 1–10 μm account for about 15% of the total volume of the solid phase.According to the plugging criteria of Barkman and Abrams (Table6), it can be seen that when the pore size of the reservoir rock is less than 3 times the particle size of the solid phase, the solid phase particles will bridge the surface of the permeable layer to form a filter cake; When the rock pore size is less than 10 times the solid particle size, the solid particles enter the reservoir near the wellbore to form shallow plugging; if the rock pore size is greater than 10 times the solid particle size, the solid particles enter the deep part of the permeable layer, increasing the depth of plugging.Table 6
Barkman and Abrams blocking criteria.
Particle size rangeDamage resultThe rock pore size is less than 3 times the solid phase particle sizeSurface bridging to form a filter cake3 times the particle size of the solid phase < rock pore diameter < 10 times the particle size of the solid phaseShallow plugging near wellboreIf the rock pore size is greater than 10 times the solid phase particle sizeDeep blockageAccording to the pore size test results of clastic rock reservoirs under different working conditions, the particle size distribution, and cumulative particle size distribution of cement slurry solid phase, it can be concluded that under the condition of no leakage, the original pore size of the reservoir is 0.1∼100μm. Among them, the pore size in the range of 1–10 μm accounts for the largest proportion, and the pore size is similar to the smaller particle size in the cement slurry. Therefore, under this working condition, the solid phase particles of the cement slurry cannot enter the reservoir. As a result, a filter cake will be formed on the surface of the reservoir core; under the leakage condition, due to the loss of the protection of the mud cake in the drilling fluid, the solid phase particles of the cement slurry will directly contact the reservoir rock. The proportion between ∼50 μm is the largest, and the part of the solid particles in the cement slurry with a solid particle size of 1 to 10 μm will enter the reservoir and form shallow plugging in the reservoir near the wellbore.


## 4. Conclusion

The protection of oil and gas reservoirs is related to various links such as exploration, drilling, completion, and development. It is a complex and systematic project, which directly affects whether the oil and gas fields can be discovered, evaluated, and efficiently developed in time, and it is also related to the development of oil and gas fields recovery rate. The damage to the reservoir is caused by the high-pressure difference between the annulus and the formation, the high fluid loss, and the high solids content of the cementing slurry during the cementing process. In this paper, taking a typical clastic rock block in an oilfield in western China as the research object, the geological investigation of fracture development, pressure deficit, and cement slurry permeability loss in the cementing process was carried out in the reservoir, and the reservoir of clastic rock reservoir was studied. The physical properties, clay mineral characteristics, and formation water quality are analyzed. The influence of cement slurry filtrate and solid phase particles on the expansion rate and permeability of reservoir clay was tested by using a core porosity and permeability tester. XRD and SEM were used to analyze the cement slurry filtrate and solid phase. The damage mechanism of facies particles to the reservoir provides theoretical data support for the research on low-damage cementing slurry technology in clastic rock reservoirs. The main research results are as follows:(1)
The average porosity of the clastic rock reservoir in the study area is 15%, the permeability is high, the average pore size of the reservoir is between 37 and 56μm, the microfractures are developed in the reservoir section, and the porosity and permeability conditions are good, the high price of formation water. The cations and inorganic ions in the filtrate generate inorganic scales such as CaCO3 and Mg(OH)2, which cross-link with the dissolved macromolecular polymers to form flocculation substances, which cause the filtrate to damage the reservoir. Hydration, tightly bonding the inert external admixture and the clastic rock formation, forms a tight sealing layer, which drastically reduces the reservoir permeability.(2)
The expansive clay particles in the reservoir absorb the moisture of the cement slurry filtrate and expand, increasing the volume of the particles. The porous formation containing expansive clay minerals absorbs moisture and causes internal expansion, and the volume expansion rate can reach 9%, which will eventually cause the reservoir to expand. The decrease of the porosity and permeability of the layer will cause damage to the reservoir; the damage to the reservoir caused by the solid particles in the cement slurry is mainly due to the blockage of the reservoir pore throats and the cement particles caused by the external admixtures in the cement slurry that do not participate in the hydration reaction. In the hydration consolidation inside the reservoir, under the condition of no leakage, the solid phase particles of the cement slurry form a filter cake on the surface of the reservoir core and cannot enter the reservoir. For the protection of the mud cake, the part of the solid particles in the cement slurry with a particle size of 1–10μm will enter the reservoir and form shallow plugging in the reservoir near the wellbore. The work serves as an important reference to green synthesis and metal oxide composites.



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*Source: 8937828-2023-02-04.xml*