New Technique Improves Steam Stimulation Completions
- F. Conrad Greer (Home-Stake Production Co.) | S.H. Shryock (Halliburton Co.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- July 1968
- Document Type
- Journal Paper
- 691 - 699
- 1968. Society of Petroleum Engineers
- 1.14.1 Casing Design, 4.6 Natural Gas, 2 Well Completion, 5.4.6 Thermal Methods, 1.10 Drilling Equipment, 1.14.3 Cement Formulation (Chemistry, Properties), 1.14 Casing and Cementing
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Production stimulation by steam injection has created many severe well problems, both before and after steaming. A completion technique has been developed that minimizes the difficulties frequently associated with high temperature injections, such as caving failure, cement failure, cement bond breakdown, and sloughing of formations in uncemented upper segments of the hole.
A casing design procedure is presented. Information is given on the material compositions employed to resist the stresses and strains of intermittent pressure and heat exposure. Field data are used to help evaluate the technique. The approach entails the placement of thermally competent cements behind the pipe, but allows the casing to expand and contract in response to temperature change. Jobs have been performed where this design has withstood steam injection down the casing without the use of packers or insulation at wellhead temperatures up to 668F and pressures up to 2,500 psig.
Thermal recovery techniques have increased the probability that wells producing low gravity crude oil will be subjected to elevated temperatures at some point in their life. Although economics may justify the drilling and completion of a low gravity oil well for primary production, many operators will make provisions for eventual high-temperature exposure. Failure to make these provisions in the original well design may lessen the economic success of stimulation and secondary recovery techniques that are presently being used or yet to be developed.
Thermal methods are being employed in many wells that were completed long before the hot techniques were known or thought feasible. In other instances wells that are thermal stimulation candidates are being completed without regard for the potential high temperature exposure. In these cases thermal loading difficulties are to be anticipated. However, experience has shown that the problems are not restricted to lack of forethought alone. Casing designs, ostensibly engineered to weather the severe stresses associated with high temperatures, have failed because of material flaws, cementing problems, human error or simply because of unforeseen factors.
The failures encountered arise from the difficulty in translating the true field conditions into the theoretical environment. Similarly, it is generally impossible to exercise the desired control on the conditions governing the drilling and completion of a well. To compensate, it is common practice to employ safety factors in design, which will adequately protect against all eventualities. However, the engineer is severely handicapped with this approach in designing a well for thermal application. The ordinary manifest of oil field goods does not contain the materials needed to achieve these high safety factors; or if the materials are adequate, it is difficult to obtain the additional necessary design specifications. The engineer has had to accept a lesser margin of safety, and as a consequence, has experienced more frequent well failure in thermal operations than in other production stimulation methods.
This paper presents a high temperature well completion technique, employing ordinary materials with minimal safety factors, which has presently proven competent to withstand the stresses imposed by saturated steam at 2,500 psig and 668F.
Present well design relies on maximum free casing movement to minimize high temperature-induced stresses. The necessity for bonding any well casing in place is even greater in a well that will be thermally stimulated. The casing must be bonded securely, in at least one section, to segregate the fluids that might be subjected to interzonal flow. This single bonded section is at the top of the pay zone, which is also at the shoe of the casing. The design has two distinct parts: the "stress section" and the "slip section". (See Fig. 1.)
The stress section is characterized by high strength materials that ultimately may be stressed to their limit of safety during thermal stimulation.
The slip section is designed to slide up and down in response to temperature changes, avoiding potentially destructive stresses. The materials employed in the slip section are selected primarily for their function. The second consideration is economy.
An examination was made of the casing at three steps in the anticipated history of the well. Stress conditions are considered at the time of cementing, when the slip section first releases, and at the most severe steam conditions.
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