Abstract

New lightweight cement technology, based on increased cement fineness, has been developed in response to problems associated with cementing primary oilfield casings in cold environments. When low density slurries are required at low temperature conditions, adequate compressive strengths may be difficult to obtain. The new technology presented in this paper, called ultrafine cement, offers lightweight cement slurries paper, called ultrafine cement, offers lightweight cement slurries (10.0 lb/gal-13.0 lb/gal) which exhibit much higher early compressive strengths than conventional lightweight systems when cured in cold environments (40 deg. F - 80 deg. F).

By means of laboratory investigation, this paper introduces ultrafine cement as a unique lightweight primary cementing material. Performance properties of ultrafine slurries are discussed and comparisons to commonly used lightweight cements are presented.

Introduction

Cementing oilfield casings in cold environments has been a challenge to field operators for many years. The in capability of cement slurries to gain early compressive strengths in these operations has led to increased research efforts and development of various types of accelerated cement compositions. Low temperature cement designs and proper cementing techniques, from the permafrost of the Alaskan North Slope to the cold waters of offshore exploration, have been documented extensively. Few papers, however, have been written on the performance of lightweight cement slurries in cold environments because very few lightweight cement slurries are available which can perform under low temperature conditions.

Recent advancements in particle size technology, however, have yielded a new ultrafine cement that performs with exceptional results at low temperatures. Tested in the laboratory from 40 deg. F to 80 deg. F, ultrafine cement slurries exhibit early compressive strengths more rapidly than conventional lightweight slurries of equal density.

Ultrafine cement technology was introduced initially to oilfield operations for remedial cementing. While use in this area continues to grow, refinement of the cement in both its physical and chemical properties has resulted in particle sizes physical and chemical properties has resulted in particle sizes that are 10 times smaller than standard oilfield cements. Increased surface area, requiring significantly more water, results in a low density mix, ideal for use in lightweight primary cementing applications.

The advantages of ultrafine cement for primary uses include less waiting-on-cement (WOC) time, a stronger cement sheath during drillout, simple slurry design - (cement and water), and other secondary benefits.

A detailed discussion of the properties and applications of ultrafine cement for primary cementing are presented in this paper. Also presented is a review of lightweight cement paper. Also presented is a review of lightweight cement compositions currently used in cold environments, including performance comparisons to ultrafine cement. performance comparisons to ultrafine cement.

LIGHTWEIGHT CEMENTS
General

Lightweight cements play a vital role in primary cementing operations. A prime reason for the use of lightweight cement is the reduction of hydrostatic pressure when cementing across a weak formation. Other uses for lightweight slurries include preventing lost circulation during pumping operations, preventing lost circulation during pumping operations, eliminating "fallback" after the cement is placed, cementing long annular columns, or as a "filler" cement to lower costs.

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