Cementing casing strings in deep water offshore wells

Abstract

The present invention provides improved compositions and methods for cementing casing strings in deep water offshore formations penetrated by well bores. The methods are basically comprised of the steps of preparing a cement composition comprised of hydraulic cement, water, an environmentally degradable water reducing and dispersing additive, an environmentally degradable set retarding additive and an environmentally degradable compressive strength and set accelerating additive.

Description

[0001] This application is a continuation-in-part of Application Ser. No. 09 / 501,337filed Feb. 9, 2000 which is a continuation-in-part of Application Ser. No. 09 / 353,676 filed Jul. 15, 1999.[0002] 1. Field of the Invention[0003] The present invention relates to cement compositions containing environmentally degradable additives and methods of cementing in subterranean zones therewith, and more particularly, to such cement compositions and methods of using the compositions for cementing conductor or surface casing strings in deep water offshore wells.[0004] 2. Description of the Prior Art[0005] In carrying out completion operations in oil and gas wells, hydraulic cement compositions are commonly utilized. For example, hydraulic cement compositions are used in primary cementing operations whereby casing strings are cemented in well bores. That is, a hydraulic cement composition is pumped into the annular space between the walls of a well bore and the exterior of a casing string dispos...

AI Technical Summary

Benefits of technology

[0017] It is, therefore, a general object of the present invention to provide improved well cement compositions containing environmentally degradable liquid additives and methods of cementing casing strings in wells using the compositions.

[0020] The present invention provides improved well cement compositions containing environmentally degradable additives and methods of cementing a casing string in a deep water offshore formation or zone penetrated by a well bore using the cement compositions. The cement compositions are comprised of a single hydraulic cement, water and additives which are all environmentally degradable and which can all be added to the water or cement slurry in liquid form. The cement compositions of this invention can be utilized over a broad temperature range, e.g., from about 32.degree. F. to about 80.degree. F. by simply changing the weight ratio and quantities of certain of the components in the compositions. Further, the cement compositions can meet the generally accepted requirements for cementing casing strings in deep water offshore wells, namely, a cement composition density in the range of from 10 to 12 pounds per gallon, a thickening time of from 3 to 5 hours and compressive strengths of from 400 psi to 600 psi at 45.degree. F. to 55.degree. F. The methods allow the operator of an offshore platform to keep a single dry cement in bulk storage on the platform along with the other components of the cement composition which except for the gas utilized to foam the composition can all be in liquid form. The liquid additives can be added to the water or the single cement slurry just prior to cementing whereby the operator uses only as much dry cement and liquid components as are needed without generating waste and losing time by changing cements, etc.

Problems solved by technology

Primary cementing operations in deep water offshore wells are particularly difficult in that they are carried out in well bores which penetrate formations between the sea floor or mud line and a depth generally under about 2,000 feet below the mud line.

Such formations are often not well consolidated, readily fracture and often have highly pressured water flows therethrough.

Another problem involved in deep water offshore well cementing is the temperature at which the cement composition must set.

However, a problem in the use of set and strength accelerating agents is that they often cause the cement compositions to have thickening times which are too short to allow placement of the cement compositions in the formations or zones to be cemented.

Another problem associated with offshore wells involves the use of dry additives such as set and compressive strength accelerating agents, set retarders, dispersing agents and the like in the cement compositions used.

As a result, unused portions of specific cement blends have to be discarded and replaced with newly prepared blends.

Again, this procedure wastes time and money in that it involves additional trips between the on-shore blending facility and the drilling platform etc.

Another problem which has often heretofore been encountered in deep water offshore well cementing is the inflow of formation fluids, e.g., water, gas and / or oil, into a cement composition which has been placed in the annulus between a casing string and the walls of a well bore, but which has not yet set.

Such inflow of formation fluids is generally caused by the cement composition becoming partially self-supporting and the consequent loss of the ability of the cement column in the annulus to transmit hydrostatic pressure.

The loss of the ability of the cement column to transmit hydrostatic pressure can result from the cement composition having too long a transition time, i.e., the time interval between when the cement composition begins to develop static gel strength and when the cement composition has sufficient gel strength to prevent the inflow of formation fluids.

At the low temperatures encountered in offshore wells, it has heretofore been difficult if not impossible to shorten the transition times of cement compositions enough to eliminate formation fluid inflow and the problems associated therewith.

Another problem encountered in offshore well cementing involves the use of additives such as water reducing agents, dispersing agents, foaming and foam stabilizing surfactants, set retarding agents and the like which are not environmentally degradable.

That is, when cement composition additives which are not fully degradable in the environment are utilized in offshore applications they find their way into the seawater and interfere with aquatic life cycles therein.