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Factors Affecting Cementing Quality in Daqing Oilfield

2022-06-21

Factors Affecting Cementing Quality in Daqing Oilfield

 

Cementing work plays a very important role in oilfield work, and cementing is still a one-time project. When there are some mistakes in cementing work, it is prone to irreparable situations. Even if there is a chance to remediate, it may not necessarily meet the sealing qualification, which will also cause unpredictable economic losses. Therefore, it can be seen that the cementing quality is directly related to the overall work quality of the oilfield. Therefore, through the analysis of the practical experience of cementing in Daqing Oilfield, several factors that can affect the cementing quality of Daqing Oilfield are found. It is hoped that this will improve the cementing quality of Daqing Oilfield.

 

1 The question is raised

 

1.1 Study the reasons that affect the cementing quality of Daqing Oilfield

 

This is because cementing works are usually one-off projects, so once some negligence or omission occurs, it may cause irreparable losses. And even if it can be recovered, it may not necessarily be qualified for sealing. Just as the target formation in Daqing Oilfield is the Guantao Formation, which is also a set of fluvial facies sedimentary formations. At the same time, it may also cause loose cementation due to the shallow depth of sandstone burial. The oil layer is mainly concentrated in the lower part of the Guantao Formation, which is closer to the large set of water layers. Drilling may cause some situations such as the expansion of the well diameter, which will greatly affect the quality of cementing.

 

1.2 Construction difficulties caused by cementing quality problems

 

At the same time, during the drilling process of Daqing Oilfield, some phenomena such as well kick and lost circulation may be encountered, which may bring difficulties to cementing and make it difficult to guarantee the quality of cementing. The cementing quality problem in some oilfields is the main problem encountered in drilling. When the reservoirs in the well section of the target layer are developed, the local water source has a high salinity, and the cementing equipment may be outdated at that time. As a result, the average density of the cement slurry in the oil reservoir section is less than 1.85 g/cm. The occurrence of this situation may seriously affect the exploration, development and utilization of this area.

 

2 Main factors affecting the cementing quality of Daqing Oilfield

 

Generally speaking, several main factors that generally affect the cementing quality are the quality of the wellbore, the structure of the wellbore, the performance of the drilling fluid, the system of the cement slurry and the construction of the cementing site. Through the analysis of Daqing Oilfield, several main factors that can affect the cementing quality of Daqing Oilfield are obtained.

 

2.1 Characteristics of the formation

 

The so-called formation characteristics are a very important factor that can affect the cementation quality of the second interface of the cement sheath, especially in the well section of the more active water layer and oil layer, the formation fluid will invade it during the solidification process of the cement slurry. contamination, which may affect the cementitious strength of the cement stone and the formation. At the same time, on the other hand, for oil and gas water layers with high permeability, the cement slurry is also prone to lose free water during the thickening process, which will also cause the pulverization of the cement slurry, resulting in the volume of the cement slurry. The reduction of , may also form micro-gap, and when this happens, it will also affect the quality of cementing.

 

2.2 Properties of cement paste

 

In addition to the characteristics of the formation will greatly affect the quality of the cementing, the performance of the cement slurry also plays a very critical role in the quality of the cementing. The performance of the cement slurry also includes the water loss of the cement slurry. The density of the grout and the rheology of the grout. When the water loss of the cement slurry is too large, it will also cause the free water when the cement solidifies to seep into the ground, which will reduce the volume of the cement slurry, which will greatly affect the The quality of cementing. Especially in medium and high permeability formations, this effect will be more obvious. At the same time, due to the large amount of water loss of the cement slurry, not only a very serious construction pump accident may be caused during the construction process, but also when the cement slurry passes through the oil and gas layer, the filtrate of the cement slurry and the particles of the cement will enter into a large amount. Among the oil and gas layers, when this happens, it is possible to contaminate the oil layer by blocking the channels of oil and gas. The density of the cement slurry will also directly reflect the size of the water-cement ratio. This is because when the cement stone is in the process of curing, only 25% of water is needed to form solidification, and the density of the cement slurry with a water-cement ratio of 25% reaches 25%. Above 2.3 g/cm3, cementing cannot be pumped. At the same time, in order to meet the requirements of cementing, we can only increase the ratio of water-cement ratio, but if the density of the cement slurry is too small, it will inevitably increase the loss of water, which will greatly affect the cementation. the quality of the well.

 

2.3 Volume shrinkage of cement stone

 

If in the process of cement hydration, once the clinker of cement and water react chemically, then the volume of the products they generate will be smaller than the total volume before hydration, and the volume of pure cement hydration will be less than The shrinkage rate can even reach 5%, and when this happens, when the volume shrinkage of the cement slurry is not well controlled, it will inevitably cause the cement stone and casing, cement stone The degree of cementation of the two interfaces with the wellbore is reduced, which will directly affect the quality of cementing. This is also a very important factor affecting the cementing quality, which needs our attention.

 

3 Several methods to improve cementing quality

 

3.1 In loose and high-permeability formations, a water-locking agent can be used to add

 

Expansion agent cement slurry system

 

Since the characteristics of the formation are an important factor affecting the cementing quality of Daqing Oilfield, we should start with the characteristics of the formation. In the relatively loose and easily permeable formations, a system of water-locking agent plus expansion agent cement slurry can be used. Since the target layer of Daqing Oilfield is the Guantao Formation, the permeability of this area is relatively high according to the characteristics and characteristics of the strata in this area, so the method of using water-locking agent and expansion agent is still very feasible. And through some specific experiments, it can also be shown that if it is under the protection of 80 °C, when we add some water-locking and anti-channeling cement admixtures to it, the toughness of these cement stones will also be to a certain extent. Improved. At the same time, the system of cement slurry using water-locking agent and expansion agent will show low consistency at high temperature and high pressure, but good rheology and good thixotropy. At this time, the early strength development of cement stone during setting It can also effectively avoid the interference of oil, gas and water invasion that may occur during the cement slurry coagulation process. At the same time, when the expansion agent is added, some volume reduction caused by cement solidification can be reduced, and the quality of the cementation between the cement sheath, the formation and the casing can also be improved. It has relatively strong impact resistance and relatively strong compression resistance. It can effectively avoid some cement sheath cracks caused by perforation impact.

 

3.2 Use some high density, low water loss and high consistency

 

cementing

 

Since the performance of the cement slurry is also an important factor that can affect the cementing quality, it is possible to use some cement slurry with high density, low water loss and high consistency for cementing. According to the field construction experience, the use of high-density cement slurry (1.95-2.0g/cm3), low-water loss cement slurry (<100 ml) and the sealing of the main oil layer should be promoted in the construction process. In order to better ensure the quality of cementing, the thickening time can also be shortened as much as possible under the condition of satisfying the construction conditions, thereby reducing the erosion effect of oil and gas water layers on the cement sheath.

 

3.3 Strengthen the quality management in the cementing process

 

In the process of cement hydration, chemical reactions may occur, which may result in volume shrinkage of the cement stone, which will easily reduce the degree of cementation and directly affect the quality of cementing. Therefore, it is necessary to strengthen the quality management during the cementing process, so as to gradually reduce the impact on the cementing quality. First of all, what needs to be done is to strictly supervise the mixing process of cement, and at the same time, conduct sampling tests on the mixing process of dry cement, not only to control the thickening time of cement slurry, but also to grasp the loss of cement slurry The amount of water, also pay attention to the degree of compression of the grout, and check the fluidity of the grout. In addition to paying attention to the problems of these raw materials, it is also necessary to strictly control the monitoring work during construction. It is necessary to strictly monitor the cementing construction process and the density of the cement slurry. It is necessary to configure the spacer fluid according to the design requirements, so as to make the performance more stable and the quantity is sufficient. To control the density and quantity of high-density, low-density grout. At the same time, it is necessary to control the displacement of the mud process, and adjust the displacement of the mud according to the pressure change to avoid cementing accidents. To sum up, there are many factors that can affect the cementing quality of Daqing Oilfield. Therefore, in the process of construction, we must think about the characteristics of Daqing Oilfield, pay attention to various problems that are prone to occur during construction, and avoid Find out a solution, so as to gradually reduce several factors affecting the cementing quality of Daqing Oilfield, so that Daqing Oilfield can get better development.