PEGS- Petroleum Engineering and Geoscience students

𝗖𝗮𝘀𝗶𝗻𝗴 𝗮𝗻𝗱 𝗧𝘂𝗯𝗶𝗻𝗴

Casing and tubing strings are the main parts of the well construction. All wells drilled for the purpose of oil or gas production (or injecting materials into underground formations) must be cased with material with sufficient strength and functionality.

1. Casing
Casing is the major structural component of a well. Casing is needed to:
▪️Maintain borehole stability
▪️Prevent contamination of water sands
▪️Isolate water from producing formations
▪️Control well pressures during drilling, production, and workover operations

Casing provides locations for the installation of:
▪️Blowout preventers
▪️Wellhead equipment
▪️Production packers
▪️Production tubing

The cost of casing is a major part of the overall well cost, so selection of casing size, grade, connectors, and setting depth is a primary engineering and economic consideration.

2. Casing strings
There are six basic types of casing strings:
▪️Conductor Casing
▪️Surface Casing
▪️Intermediate Casing
▪️Production Casing
▪️Liner
▪️Liner tieback casing

3. Tubing
Tubing is the conduit through which oil and gas are brought from the producing formations to the field surface facilities for processing. Tubing must be adequately strong to resist loads and deformations associated with production and workovers. Further, tubing must be sized to support the expected rates of production of oil and gas. Clearly, tubing that is too small restricts production and subsequent economic performance of the well. Tubing that is too large, however, may have an economic impact beyond the cost of the tubing string itself, because the tubing size will influence the overall casing design of the well.

4. Properties of casing and tubing
The American Petroleum Inst. (API) has formed standards for oil/gas casing that are accepted in most countries by oil and service companies. Casing is classified according to five properties:
▪️The manner of manufacture
▪️Steel grade
▪️Type of joints
▪️Length range
▪️The wall thickness (unit weight)

𝗪𝗲𝗹𝗹 𝗦𝘁𝗶𝗺𝘂𝗹𝗮𝘁𝗶𝗼𝗻 𝗢𝗽𝘁𝗶𝗺𝗶𝘇𝗮𝘁𝗶𝗼𝗻
Well stimulation optimization refers to the systematic evaluation and refinement of stimulation techniques to maximize reservoir productivity. The goal is to create or restore pathways for fluid flow within the reservoir, removing restrictions and improving the connectivity between the wellbore and the surrounding formation.

Key Techniques and Methods for Well Stimulation Optimization:

1. Hydraulic Fracturing:
Hydraulic fracturing, or fracking, is a widely used technique that involves injecting high-pressure fluids into the reservoir formation. This creates fractures and fissures, which enhance permeability and allow for improved fluid flow towards the wellbore. Key aspects of hydraulic fracturing optimization include fluid selection, proppant placement, and fracture size and orientation control.

2. Matrix Acidizing:
Matrix acidizing involves pumping acid into the reservoir formation to dissolve and remove materials, such as mud, scale, or formation damage. Acidizing helps stimulate near-wellbore formation, improving permeability and increasing the well's production rate. Optimization in matrix acidizing includes acid selection, injection rate, and the use of corrosion inhibitors to prevent damage to well equipment.

3. Water and Gas Shut-Off:
Water and gas coning and breakthroughs can significantly impact well productivity. By utilizing selective plugging techniques, such as through the use of chemical diverters or mechanical packers, operators can optimize reservoir performance. This involves identifying the key water and gas-producing zones and deploying blocking materials or resins to restrict undesired fluid flow and prevent reservoir depletion.

4. Reservoir Zonation:
Understanding the heterogeneity of reservoirs is crucial for well stimulation optimization. Reservoir zonation involves dividing the reservoir into different zones based on lithology, fluid properties, and geological formations. By targeting specific zones for stimulation, engineers can enhance productivity in the areas that offer the highest potential for recovery. This technique is often combined with advanced reservoir characterization techniques, such as well logging and seismic imaging.

5. Intelligent Well Completions:
Intelligent well completions involve deploying advanced technologies, such as inflow control devices (ICDs) and autonomous inflow control devices (AICDs), to optimize fluid flow rates along the wellbore. These devices adjust flow rates based on reservoir pressures and fluid properties, allowing for better control and management of production. Intelligent well completion optimization includes the selection of suitable devices and their placement along the wellbore.

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