Cementing Solutions for Corrosive Well Environments

Abstract

Main factors which are responsible for the corrosion of the cement sheath in wells are determined based on lab tests and field analyses from a literature survey. A description of the chemistry, mineralogy, physical properties of API well cements and their mechanisms of corrosion in the presence of aggressive formation and injection fluids (such as magnesia or sulfate containing brines and CO 2 ) are given. API cement hydration mainly produces Calcium-Silicate-Hydrate (C-S-H) phases, which are responsible for the strength, and portlandite "Ca(OH) 2 " which is basically a weak point within the cement matrix. Increasing permeability and portlandite content reduce strength and chemical resistance of set cement towards corrosive media. The addition of pozzolanic materials eliminates portlandite and allows lowering the water content in the cement system. Both effects can reduce the permeability and improve the mechanical properties of set cement. Cement specimens were prepared and exposed to CO 2 loaded water at 300 °F and 3,000 psi for 6 months. Mechanical properties tests, microscopy, and quantitative CaCO 3 analyses revealed significantly less corrosion and negative impacts for an API cement-pozzolan blend compared to a conventional API cement design at same density. Practical and economical concepts for improvements of the cement sheath with respect to cement slurry design, cementing process and the impact of factors such as temperature or cement admixtures are presented to mitigate cement corrosion.1. Understand the mineralogy, chemistry, and physical properties of set API cements. 2. Study the mechanisms of different corrosion types for API cements and potential solutions based on a literature survey. 3. Design and test an "pozzolan" API cement system in comparison to a "conventional" system for a corrosive well scenario (CO 2 , BHST 300 °F, 3,000 psi) with occurring mechanical downhole stresses. 4. Compose necessary cementing guidelines for corrosive well environments.

An Experimental Study on Effects of Static CO2 on Cement under High-Pressure/High-Temperature Conditions

“…The interaction between cement and CO 2 in the rocks has gained significance in recent years Moroni et al 2009;Brandl et al 2010;Le Guen et al 2008). Geological storage of CO 2 in depleted and partially depleted oil fields has gained increasing global interest as an economically viable means of reducing CO 2 emissions, while recovering extra oil.…”

A Diffusion Controlled Model for Prediction of Long-Term Cement Sheath Carbonation

“…The respective concentration of the different species is given by the dissociation constant of carbonic acid in water. Decomposition of cement occurs in two distinct steps, as visually observed in experiments conducted by Duguid and Scherer (2010) and Brandl et al (2010). These two steps are (1) carbonation and (2) calcium carbonate dissolution, which are explained in the following.…”

Characterization of the unidirectional corrosion of oilwell cement exposed to H2S under high-sulfur gas reservoir conditions

“…The load for testing was 100 g, and the hold time was 10 s. Porosity and permeability affect the hydraulic integrity of cement sheath. [19][20][21] Porosity of the cement samples before and after the corrosion was determined by mercury intrusion porosimetry (PoreMaster-60, Quantachrome, USA). Gas permeability of the cement samples was determined using a gas permeability tester (DKS-3, Hai'an Petroleum Instrument, China) according to Darcy's law.…”