The Importance of Cementing in the Oil & Gas Industry
The presence of silica fume for wellhead cementing is a critical component of hydraulic fracturing, also known as “fracking” or “fracing.” Fracking is a relatively new oil drilling process that unearths deposits of natural gas or oil from deep within the earth by pumping a fluid mixture of water and other proppants into the existing cracks and fissures within the producing zone via hydraulic pressure, expanding existing, as well as creating additional, cracks and fissures in the earth to obtain the targeted oil or natural gas. Once the pressurized fluid is removed, the remaining proppants are left behind to keep the cracks and fissures open, which will allow the natural gas or oil to move more easily. This page will discuss how the oil and gas industries depend on silica fume for wellhead cementing to maximize production levels and minimize gas migration.
Drilling The Well & Casing Types
Before any oil or gas can be harvested from beneath the surface, a vertical or horizontal well must be drilled depending on the specific depth of the producing zone. Drilling cannot be done as one continuous shaft, but instead as a series of varying-sized shafts that progressively shrink from large diameter shafts down to a smaller diameter shaft that terminate in the producing zone. This drilling process requires adding varying types of casing that help to provide the requisite strength to the sides of the drill shaft and eliminate the potential of cave-ins and other debris entering the drill shaft that would impact performance. The drill shaft begins at the surface starting with the conductor casing, followed by the surface casing, intermediate casing, and ends with the production casing. Each casing provides a unique function and purpose.
Surface Casing: This casing protects concealed freshwater zones, controls gas and fluid movement, cases off unconsolidated formations and lost circulation zones, provides a place to nipple up to the BOP’s and to attach surface equipment, and provides support for the deeper sections of the casing.
Intermediate Casing: This casing seals off large amounts of the open hole and protects it from increased mud weight, blocks off the gas, water, salt, shale, and lost circulation and troublesome zones, protects and controls pressure zones, and provides a place to hang a production liner.
Production Casing: The final casing placed in the drill shaft is the production liner which cases off the gas, water, salt, and shale zones, provides control of the well at the wellhead for production and pressure controls, protects pay zones from unwanted fluids, and provides a place to change out drill fluids to completion fluids.
Using Silica Fume for Wellhead Cementing
Cement enhanced with silica fume is introduced when the well shaft is drilled to the casing point, and the casing has been set. This primary cement will be used to fill the annulus around the casing after the mud and dirt surrounding the casing have been pumped out. Primary cementing is completed to seal the wellbore from zones containing oil, gas, and water. Another purpose of primary cementing is to fix the casing securely to the side of the well shaft. Water, dry cement, and special additives are mixed to create the cement used during this process.
The cement is moved down and through the casing by a high-pressure cement pump. The top of the casing contains the cementing head, which allows the cement to be introduced into the pump where the crew can control the volume and speed at which the cement is dispersed. The cementing head also holds the bottom wiper plug that is used to wipe off the mud from the casing that separates the mud from the cement and the top plug that will clear the remaining cement from the displacement fluid cement. Displacement fluid is also dispersed through the cementing head which then will create pressure and position the cement into place.
The float collar is attached to the bottom of the casing where it will help hold the casing in place. When the cementing has begun, pressure from the cement pump sends the cement and the bottom wiper plug down through the casing, and once the bottom wiper plug is in place, pressure from the cement ruptures the bottom wiper plug allowing the cement to go out through the guide shoe and fill the annulus between the casing and the wall of the shaft. After the determined amount of cement has been dispersed, the top wiper plug is released and pressure from the displacement fluid pushes the top wiper plug to the bottom of the casing that will rest on top of the bottom plug creating a seal. This finishes dispersing the cement into the annulus. The float valve then holds the cement in place and does not allow it to re-enter the casing. Depending on the type of cement and the mixture used the typical time that it will take for the cement to harden is between 12 to 24 hours, which then completes the cementing process.
Applications of Silica Fume for Wellhead Cementing
The importance of silica fume for wellhead cementing in the oil and natural gas industry is paramount to keeping workers safe and maximizing overall production. In the oil industry, silica fume can be used as an additive to traditional concrete for primary applications such as the grout used in hydraulic sealing of the well bore. The enhanced grout mixture, once cured, offers an improved and condensed internal matrix that mitigates the loss of gas to the surrounding environment. Not only does this help maximize well productivity, but it can be an incredible resource for meeting specific environmental regulations and preventing the leaching of dangerous chemicals or oil into the surrounding area.
Silica fume may also be used in secondary applications like repairing leaks throughout the well, addressing efficiency-killing splits, and effectively sealing off depleted zones. When used in the natural gas industry, the microscopic particle size of silica fume works as a blocking agent in oil well grout that prevents gas migration and helps increase well productivity.
Working with R-E-D Industrial Products
In the oil and gas industry, incorporating premium quality silica fume into wellhead cementing and other concrete structures significantly enhances their strength, durability, and long-term performance. Given the industry's challenging operating conditions and growing environmental regulations, improving wellbore cement with silica fume is crucial to maximizing safety, and performance, and preventing possible shutdowns. R-E-D Industrial Products is well–versed in the many challenges of using silica fume for wellhead cementing and our experienced team is readily available to learn more about your specific applications and can provide a detailed quote with industry best lead times and competitive costs.
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