Planning the Well Construction Process for the use of Solid Expandable Casing

Abstract

In the past, solid expandable casing technology has often been successfully used as a contingency measure to minimize the loss of hole size while dealing with drilling problems. Other applications, such as overall reduction of casing string sizes and numbers, sidetrack applications, and production conformance applications have been slower to attract interest, even though they are all technically viable and economic. This paper will investigate the process for successfully integrating solid expandable tubulars into all aspects of the well construction program. Preparing the hole section for the installation of the solid expandables will be discussed. Drilling, completion, and production operations through expanded tubulars will also be reviewed. The process of planning solid expandable projects from conception through well design will be investigated, focusing specifically on the ancillary technologies in the drilling, completion, and production phases. When all aspects of the well construction are optimized, the greatest economic value of solid expandables is achieved at the minimum operational risk. Optimizing the Casing Design There are several avenues to consider when optimizing well design with expandable casing. Opportunities exist to save resources merely by reducing the casing size itself. In addition, optimization changes are available by drilling in the most favorable size ranges: not too small, and not too large. Reductions in size of the hole drilled generally result in savings. Reduced deliverability and flexibility in the smaller wellbore is balanced by savings in top side costs, such as location or platform costs, tubular costs, and mud products costs. Current costs from operators in the Middle East indicate that these savings are on the order of 20 to 40% when one full casing size is eliminated. As technology improves, it increases the the length of producible sections and enables the operator to place wells in the optimum spot in a pay zone. As a result, operators are increasingly reluctant to compromise deliverability with a small final hole diameter. In addition to the deliverability issue, a conventionally-drilled slimhole design lacks some flexibility to manage with unexpected well problems. If a serious lost circulation zone or an overpressured zone is encountered, there may not be enough diameter remaining in the existing hole to drill the well to total depth. There may also not be enough room left to deal with corrosion or cement isolation problems. In general, there are specific hole sizes that are more cost effective to drill than other hole sizes. For example, it is generally accepted that hole sizes below 7–7/8 in. are generally more difficult to drill than larger sizes. Smaller bits and other bottomhole assembly (BHA) parts can be less durable due to their smaller mass. The assemblies are also quite flexible, which can lead to drag and buckling problems. The lack of space available to design engineers can mean that stress concentrations may not be easily removed from parts and that re-enforcing may not be simple. In items that have moving parts, like roller cone bits, roller reamers, and other downhole tools, there is difficulty scaling down parts due to size, strength, and heat dissipation issues. Scaling down can lead to problems dissipating heat that, in turn, reduces the bearing and cutting structure life. Similarly, hole sizes above 12 inches tend to be challenging to drill because scaling up all the components of the drilling BHA is difficult and expensive. Typically only the bit and a few collars and stabilizers will be near the hole size. Every other part of the drillstring will be undersized. Undersizing leads to pump and hydraulics problems such as annular velocity needed for hole cleaning, cuttings loading, and equivalent circulating density. There is also the sheer size of the hole to consider. Larger holes require more drilling mud, a bigger volumetric flow rate, larger pumps, more solids control equipment, more waste disposal, and more expensive BHA parts. Lastly, and probably most important, the larger hole sizes require more rock to be crushed and removed, more steel for casing, and more cement for zonal isolation.

Reducing Non-Productive Time Through the Use of Solid Expandable Tubulars: How to Beat the Curve Through Pre-Planning

“…It is also generally easier to model and control directional BHAs as one moves toward the optimum sizes. 1 Smaller assemblies not only drill slower, but are much less reliable than larger assemblies at deeper depths. This early changeout to a smaller drilling assembly due to further reduction in hole size, or because of an additional string of pipe, adds to both flat time and lower penetration rates.…”

Application of Simulation Technology on the Design of One Special Expandable Tubular Thread

“…In the process of drilling, by the ends of the casing threads connection, the casing strings are constructed to seal formation and build borehole channel. Expandable casing technology is a key technology of oil drilling industry in 21 st century [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] . Its technical principle is to increase borehole diameter by casing string's radial expansion to plastic deformation area, so as to save borehole diameter, as shown in figure 1.…”