Cementing is a critical operation in the well construction process. As such, it is a service provided by most oilfield service companies. It is highly technical and must be performed with precision to ensure the integrity of the well. It also has substantial financial implications if done incorrectly or with substandard materials.
Cementing is the process of mixing a slurry of cement, water, and additives and pumping it down through casing to critical points in the annulus around the casing or in the open hole below the casing string.
We routinely provide cementing services for our customers at Anadarko onshore US, Anadarko’s APC (Anadarko Petroleum Corp) business unit, and Anadarko Offshore U.S.A., Inc. Additionally, we often provide real-time data analysis on current operations and assist in developing best practices for future operations to improve safety and efficiency while reducing costs.
1. Cementing is the process of mixing a slurry of cement, cement additives and water and pumping it down through casing to critical points in the annulus around the casing or in the open hole below the casing string. The primary function of this cement sheath is to bond and support the casing and provide zonal isolation. Cement sheaths also help prevent fluid migration between geological formations, which can cause formation damage and/or lost circulation.
2. A study by the International Association of Oil & Gas Producers (OGP) found that well integrity incidents are caused mainly by human error and inadequate design, well construction, cementing and testing processes; consequently, they are largely preventable.
3. The study also reported that “the most common integrity problems are related to surface casing vent flow (SCVF) (30%), tubing leaks (25%), packer failures (15%) and casing failures (10%).”
4. To achieve well integrity, one should focus on:
• Avoiding cross flow
• Maintaining zonal isolation
• Controlling annular pressure buildup
5. Proper planning for a successful cement job starts with selecting appropriate materials. Selection criteria include proper density, thickening time, compressive strength, pumpability
1. Cement cures (hardens) under pressure, not temperature.
2. Pressure is the key to curing cement and requires pumping the slurry at a rate of 7-10 sacks/minute (or 10,000 lbs. per minute).
3. The ratio of slurry to water should be around 14:1 or 16:1.
4. Slurry should be pumped at a rate of 7-10 sacks/minute to allow the cement to cure under pressure and achieve maximum compressive strength. If you pump too slow or too fast, you will get differential thickening of the slurry and the top zone will set before the bottom zone has a chance to set up; this leads to channeling and poor cementing jobs.
5. The best way to ensure the correct pumping rate is by using a flow meter in conjunction with a chart that provides pumping rates for various sizes of cementing equipment at different pumping pressures. These charts are usually provided by your cement supplier.
6. A good rule of thumb for determining if you are pumping your slurry at the proper rate is as follows: after you have pumped 100 sacks, add more water until you have 400 sacks in the batch tank; then pump another 100 sacks out into an empty batch
Cementing is an essential operation in the completion of a well, and many of the problems encountered in production are directly related to cementing. Proper zonal isolation is important because poor zonal isolation can lead to water or gas coning, channeling, sand production and corrosion.
In order for cement to do its job properly, it should have certain properties such as compressive strength, fluid loss, thickening time and free water. For example, cement should not lose fluid while being pumped into the casing or annulus; this would result in reduced cement height. The recommended minimum compressive strength of primary cement is 500 psi. However, if the formation pressure is less than 1,000 psi above hydrostatic pressure (0.433 psi/ft), then the compressive strength of the cement must be at least 1.5 times formation pressure (1).
Thickening time should be determined in order for the cement to set before any of the mud filtrate can migrate into the formation. This will help ensure a proper bond between the casing and formation along with an effective zonal isolation. This time also allows for displacement of all mud from inside the casing before setting; otherwise, channels could form due to filtrate migration from thickened mud after cement
Cementing is a key part of the well construction process. Once the casing is run and cemented, subsequent production tubing can be lowered into the well and secured in place. If there’s a problem with the cement job, however, hydrocarbons may flow between the casing and the wellbore, causing a “lost circulation” situation that could jeopardize the entire operation. What’s more, a faulty cement job can lead to formation damage, which can ultimately mean reduced overall production.
To avoid lost circulation problems and ensure that the completed well will perform at its maximum potential, it’s critical to choose the right cement for your specific needs. There are several factors to consider when choosing a cement type:
Casing size. For most casing sizes up to 6-5/8 inches in diameter, you’ll want to use API class A or B cement. For casing larger than 6-5/8 inches in diameter, you’ll need API class C or D cement.
Depth. The deeper you’re drilling, the greater density your cement will need to withstand higher downhole temperatures and pressures.
Formation integrity test (FIT). Your contractor should perform an FIT before cementing to determine what type of material is present in your wellbore;
Correctly mixing and applying cement is key to creating a stable deck or surface. Here are some tips on how to mix cement, as well as how to apply it. If you have further questions about mixing cement, consult your local hardware store or a cement expert.
Cement is one of the most significant materials used in construction, and it has many different applications. From making concrete for a driveway to creating mortar for laying bricks, cement can do it all. It is also used to create surfaces both outdoors and indoors and can make items such as countertops and flooring when mixed with other materials. However, before you can use cement, you must first mix it with water and other ingredients to create the finished product. If you are new to working with cement or just looking for an overview on how best to mix cement, read on for some helpful tips.
The proper ratio of water to cement powder depends on the conditions in which the materials will be used. For example, if you plan on working with unheated concrete during cold weather, then you need more water than usual to make the concrete easier to work with when frozen. Similarly, if the concrete will be exposed to high heat or humidity, then less water should be used so that
The most basic type of bonding is when a cement molecule forms a chemical bond with the tooth structure. This is known as the hybrid layer or hybrid zone. The hybrid layer can be extremely strong, so strong that it can resist all forces except for shear or tensile forces. These types of forces typically occur as a result of heavy occlusal loading and are more commonly found in posterior teeth than anterior teeth. Anterior teeth are more commonly loaded with compressive forces which do not affect the hybrid layer.