The Casing String Design

The casing string mainly affords axial loads, external pressure and intrinsic pressure and in some cases they also carry tortuosity and perforation instantaneous shocking loads. In environment, the casing string is affected by corrodent of oil/gas and groundwater (H₂S, CO₂, Cl^-, [O], H₂O, etc.) as well as changing temperature. Therefore, the main form of casing failure shows collapse, decollement, leakage and break which also includes crack, burst, bad break , coupling longitudinal dehiscence, perforation cracking, stress corrosion cracking and so on.

Besides satisfying the requirements of the geologic formation, the most important of casing string design is to meet the axial load, external pressure (extruding) loads, internal pressure loads and other additional loads such as bending, friction, and temperature. Some caustic wells also need considering the triaxial loading.

Tubing String Design

Tubing string mainly holds up axial alternating loads, to some extends, it bear bending loads and it is also affected by the underground corrosion medium (H₂S, CO₂, Cl^-, [O], H₂O, etc.) and changing temperature. Therefore, the main failure mode of the flow string is decollement, break (pipe string faulting, burst, coupling longitudinal dehiscence, fatigue, stress corrosion cracking), leakage and surface damage.

Tubing string design not only considers the strength (tearing strength, collapsing strength, internal pressure strength) but also need to consider the relationship between the size and pressure，performance of tubing material anti-corrosion and tubing seal.

Structure Design of Exceptional Well Bore

Deep wells, ultra deep wells often accompany by high temperature, high pressure and complex geological condition, this time the structure of well bore using the API conventional casing often cannot achieve the intended zone safely and efficiently.

For the formation characteristics and production needs of oil and gas exploration and development blocks, targeted use of exceptional well bore with non-API conventional casing is an effective means to deal with these problems. The structure of exceptional well bore can be tailored to non-API format, steel grade and special threaded casing to protect the efficient exploitation of oil and gas.

The structure of exceptional well bore is required to design and production of non-API casing, and demonstrate the load capacity of drilling rig, the new sized borehole, the supplement of drilling tools under the casing circumstance and adapt to process parameters of the new wellbore casing structure and economic benefits of new well bore structure.

Drill String Design and Optimization

The basic goal of the drill string design is configuring a drill string to complete drilling work with expected diameter and its depth in the borehole. There are also some optimization problems which include the structure of the drill string, hydraulics and wellbore cleaning, drilling control and measurement, preventing sticking and so on. Thus the drill string design is not just a simple drill string component configuration.

Four problems of drill string design overlap and contradict each other, improving the efficacy as well as reducing its effectiveness. The only solution is to optimize drill string design. First, optimization methods are usually to choose a design grade evaluation parameter for two (or more) design to select. This grade assessment parameter can be quantitatively assessed for both designs. For example, the load factor for the choice of grade evaluation parameters, assuming other conditions of two designs can be equivalent received, then it is clear that the design of 60% load factor is better than the design of 90% load factor and the result is optimized.