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From the standpoint of drilling, our input into that process is to assess the risks and allow for alternatives. This decision is based on numerous criteria, so we assume, for our purposes, that the size of the last string is predetermined and proceed from that point. That decision usually is the function of an interdisciplinary team of reservoir, production, and drilling personnel. The size of the last string of casing run in a well generally is determined by the type of completion that will be employed. This means that, in selecting casing size, we usually start with the casing size at the bottom of the hole and work to the top.
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Hole size at any point in the well except the surface is determined by the previous string of casing.Two important things to know about selection of casing size: Gulf Professional Publishing.Once the setting depths have been determined the next step is obviously to select the sizes of the casing strings to be set. Casing and Liners for Drilling and Completion, Second Edition: Design and Application (Gulf Drilling Guides). Advanced Well Completion Engineering, Third Edition. Well Completion Design, Volume 56 (Developments in Petroleum Science). In order to determine what casing grades to be used in the well, you need do the detailed calculations based on several load cases as burst, collapse, tensile, etc. The load cases are not accounted for in this example. Note: this plan is based on size selection only. The biggest size of completion equipment is 5 inch.Īccording to the Table 1, the bit and casing plan for this well is described below.Completion equipment – TRSV, Side Pocket Mandrel, Packer, etc.The Rig needs to drill and set the conductor casing to 500’ TVD in order to rig up the well control equipment. The casing string should be set at 3000’ TVD, 6,000’ TVD and 12,000’ TVD. Table 1– Commonly Used Bit Sizes That Will Pass Through API CasingĮxample:According to the previous example, this is the casing design based on pore pressure and fracture gradient (Figure 1).įigure 1– Casing Design Based On Pore Pressure and Fracture Gradient This is based on API casing therefore if you use special casing, you may need to check with the casing company to give you exact casing ID. You may need to use the following table (Table 1) to determine bit size and casing size. Once you get the last casing string, the upper string is selected by repeating bit selection and casing selection similar to step #3 and #4. Casing size must be smaller than bit size and its ID must be bigger than the biggest component in completion string.ĥ. Bit size for drilling the production section.Ĥ. This will directly impact of production casing.ģ. Completion equipment is planned to install with tubing string. Proper sizing of tubing is determined by inflow performance analysis.Ģ. The sequence of design is based on the following steps ġ. We’ve learnt several topics in regard to casing design and this article will demonstrate you how to determine casing size in the well.Ĭasing size selection is determined from the inside outward and it starts from the bottom hole.