AmericanChemicalSociety.com

Report of Progress:

I wish to sincerely thank the ACS PRF for supporting research project on the crystallization of salts and its impact on productivity of natural gas reservoirs. The award (ACS PRF# 46375-G9) has helped me support two undergraduate students, provided summer salary and purchase of computing equipment in the first year in addition to other equipment such as software and printers. In the second year the monies in the account were used to support undergraduate student researchers, principal investigator conference travel expenses and some equipment purchases (see financial report for details).

In the first year we developed a complete model to predict salt crystallization in the pores of a rock sample including the capillary pressure and evaporative effects. The model was solved completely using numerical and analytical methods. The results were then sent to Transport in Porous Media Journal for peer review and publication. Subsequently in the second year, reviews for the paper were obtained and additional modeling and simulation were conducted to complete the reviewer comments. In addition to the proposed objectives experiments on salt crystallization were conducted to validate the model. Existing equipments from my lab, such as coreholder, mass flowmeters and other pressure transducers were used to conduct the experiments. The results were then compared with predictions which validated the capillary pressure driven film flow physical model. The paper is already accepted and published in the journal. The date of final publication is 30 May 2009.

The results of the work are being integrated with a course that I am currently teaching called Transport in Porous Media. Two of the four main objectives were achieved during the first year of the two year award including the experimental work which was not proposed but needed to complete our publication review. Because of this additional experimental work we experienced a delay in completing the remaining two objectives. We are already working on the modeling portion for the prediction of porosity and permeability in the case where the salt crystallization occurs. It is hoped that in the remaining year the remaining two objectives will be achieved and also a proposal to continue the exciting investigation of crystallization in porous media will be prepared.

The results of the study were also presented in two conferences:

1) “Evaporation in Porous Rocks: Application to Geothermal Energy Recovery,” The Alternative Energy Symposium, AAAS-SWARM meeting held in Tulsa, Oklahoma in 2009 between 28-31 March;

2) “Salt Crystallization in Porous Rocks,” paper presented at the American Chemical Society Tulsa Chapter Meeting in April 2009.

The principal investigator also attended the 13th international colloids and surface science conference which was held along with the 83rd ACS colloid and surface science symposium in Columbia University, New York, between 14-19 2009. The conference offered an opportunity to know the latest advances in the field of surface and colloid sciences and enabled the principal investigator to identify priority areas for future research directions.

It is expected that paper proposals will be made in future to present results in both chemistry related symposium such as the ACS national meeting and the Society of Petroleum Engineers conferences. Due acknowledgement to the award from ACS PRF will be made on all the publications and presentations. The achievements in the first and second year are described in detail in the following paragraphs.

Research Summary

Natural gas generally occurs along with connate brine or reservoir that is generally high in dissolved salt content. Production of natural gas is generally achieved by reducing the pressure in the bottom-hole of a well drilled into the reservoir that holds the natural gas in pore spaces. The expansion of gas during production itself can lead to an evaporative effect which can in turn lead to brine super saturation and hence salt crystallization. Halite precipitation, triggered by evaporation, is an important formation damage mechanism that affects productivity of a gas well.

Following are the main objectives of the proposed study:

1. understand the impact of flow through drying on the salt concentration in porous medium.

2. investigate the effect of capillary films on salt transport in porous medium.

3. evaluate the rate of change of porosity and permeability due to salt crystallization during flow through drying process including transport through films.

4. predict the impact of following parameters on the gas flow rate by including salt crystallization with the above model: absolute initial permeability, temperature, and pressure gradient.

In the first year, since the award was made, considerable progress was made to identify the model that describes evaporation based salt crystallization in porous samples. In particular, an evolution equation for liquid salt concentration that couples the capillary driven film flow along with the evaporative effects has been developed. Additionally an evolution equation for solid salt concentration was developed.

In the second year experiments were conducted to evaluate the impact of capillary pressure driven film flow on the evaporation and salt crystallization. Gas injection was carried out at constant pressure drop into Berea sandstone cores to carry out evaporation of the resident ionic salt solution (potassium chloride in water). The distribution of the salt in the rock cores were analyzed by gravimetric method to determine the salt wicking within the core. In the remaining time period we plan to complete the following objectives.

Objectives Remaining:

1. evaluate the rate of change of porosity and permeability due to salt crystallization during flow through drying process including transport through films.

2. predict the impact of following parameters on the gas flow rate by including salt crystallization with the above model: absolute initial permeability, temperature, and pressure gradient.