Proper Selection Of Float And Multiple-Stage Cementing Equipment Can Save Money
Authors: Sullaway Bob , Giroux Dick 
Published: March 2010

Oil and gas producers and operators can reduce well completion costs by (1) selecting lower cost float equipment for applications in which expensive combinations have been used traditionally and (2) using test procedures presented in this paper as performance standards jar selecting stage ceme1lting equipment.

Float equipment cases build to pipe specifications as outlined by the American Petroleum institute (API) and the National Association of Corrosion Engineers (NACE) can be expensive and may riot be necessary in many applications, based on the reasons listed below.Float equipment is below perforations, so it is not subject to the full effect of harsh well conditions, such as stimulation fluids, stimulation pressure formation flow that requires gas-tight casing threads, etc.Float equipment supports only one or two joints of casting, so generally equipment with a lower tensile strength can be used,Liner casing overlaps float equipment, so equipment burst ratings can be lower,

This paper explains why float equipment made with K-55 grade coupling stock Can be used with most casing grades and weights in most well conditions. The paper also presents tests Used to help evalliaie stage cementing equipment design.

These tests corer burst, collapse, functional performance, ability to withstand high flow rates, short-term seal testing at high temperatures, the effects of bending while going in a deviated hole, and the effects of compression and tension loading on equipment operation. These tests should give insight as to how design decisions for stage tools are made in the selection of (1) case material, (2) heat treatment, (3) case dimensions, and (4) seal system. In the absence of an API recommended practice (RP) document on stage cementing equipment, the information presented here can help operators make logical decisions about the type of stage tool needed for a particular well.

API and NACE Standards

Using the criteria and tests presented in this paper can help oil and gas operators make informed, money-saving decisions when selecting float and/or stage cementing equipment. First, a basic understanding of pipe grades and the limitations of different pipe grades helps operators make wise choices in selecting float and stage cementing equipment.

Specification SCT "Specification for Casing and Tubing", published by API, specifies acceptable manufacturing processes, chemical composition, and mechanical properties of API approved casing grades(3). In API nomenclature, the letter designates casing grade, and the number following the lette designates minimum field strength in 1000 psi (6.9 MPa), for example, the "N" in N-80 is the casing grade, and "80" indicates 80 000 psi (551.6 MPa) minimum yield strength. NACE has published standard covering metallic material requirements for resistants to sulphide stress cracking (SSC) for petroleum production, drilling, and flowline equipment. This document is called NACE Standard MR-OI-75-84, "Sulfide Stress Cracking Resistant Metallic rV1ateriais for Oil Field Equipment.(2) In this standard, NACE defines which API grades work ill an SSC environment and at what temperatures (Table I).