@article{zhang_zhang_gardner_liu_zhang_qiu_chen_tian_wang_2018, title={Quantitative monitoring of CO2 sequestration using thermal neutron detection technique in heavy oil reservoirs}, volume={79}, ISSN={["1878-0148"]}, DOI={10.1016/j.ijggc.2018.10.003}, abstractNote={CO2 enhanced oil recovery (CO2-EOR) project is of significance for CO2 sequestration and heavy oil recovery. Quantitative monitoring of CO2 saturation (SCO2) is essential to recognizing and understanding the migration and distribution of CO2 injected into the geological formations. In this paper, based on the difference in the neutron moderation ability of CO2, water and heavy oil, thermal neutron detection technique is applied in heavy oil reservoirs to monitor CO2 sequestration. By Monte Carlo simulation, the responses of thermal neutron count ratio versus different porosities and CO2 saturation were studied. Then, a mathematical model of CO2 saturation versus thermal neutron count ratio and formation porosity was established to quantitatively calculate CO2 saturation. Besides, the effects of formation pressure and temperature, heavy oil density, lithology, and other factors on the method were studied. Results show that variations of formation pressure, formation temperature, and density of heavy oil have little impact on the CO2 saturation measurement. However, the change of formation lithology results in larger CO2 saturation errors and needs corrections. In addition, the method has a low discrimination between CO2 and CH4 gas, and the results are easily affected by the CH4 content. Finally, a simulated case demonstrates the application of the method. For the heavy-oil sandstone with different porosities, the method shows a perfect performance: the SCO2 errors are less than 1% for the high and low gas saturated formation. This research provides an effective strategy to monitor CO2 storage and residual oil saturation in CO2-EOR reservoirs.}, journal={INTERNATIONAL JOURNAL OF GREENHOUSE GAS CONTROL}, author={Zhang, Feng and Zhang, Quanying and Gardner, Robin P. and Liu, Juntao and Zhang, Xiaoyang and Qiu, Fei and Chen, Qian and Tian, Lili and Wang, Yang}, year={2018}, month={Dec}, pages={154–164} }
 @article{liu_zhang_gardner_hou_zhang_zhang_li_li_hu_2016, title={A method to improve the sensitivity of neutron porosity measurement based on D-T source}, volume={33}, ISSN={["2212-3865"]}, DOI={10.1016/j.jngse.2016.06.028}, abstractNote={Compensated porosity logging tool utilizing deuterium-tritium (D-T) source shows a lower sensitivity to the variation of formation porosity compared with that adopting Am-Be source. In order to improve the sensitivity, the factors of an infinite homogeneous formation influencing slowing-down length and the near to far counts ratio are analyzed. Then Monte Carlo simulation method is used to build well logging models to study the responses of a neutron porosity logging tool to hydrogen index and formation density. It shows that in addition to hydrogen index, the variation of the density also has a great impact on slowing-down length and the ratio which reduces the response sensitivity to porosity. A new model depicts the relationship between the count ratio and porosity is proposed. When the model is used to process the measured ratio, the ratio shows improved dynamic range and sensitivity to porosity compared with the values without processing.}, journal={JOURNAL OF NATURAL GAS SCIENCE AND ENGINEERING}, author={Liu, Juntao and Zhang, Feng and Gardner, Robin P. and Hou, Guojing and Zhang, Quanying and Zhang, Yan and Li, Xianghui and Li, Hu and Hu, Cong}, year={2016}, month={Jul}, pages={879–884} }
 @article{liu_zhang_gardner_hou_zhang_li_2015, title={A method to evaluate hydraulic fracture using proppant detection}, volume={105}, ISSN={["0969-8043"]}, DOI={10.1016/j.apradiso.2015.08.003}, abstractNote={Accurate determination of the proppant placement and propped fracture height are important for evaluating and optimizing stimulation strategies. A technology using non-radioactive proppant and a pulsed neutron gamma energy spectra logging tool to determine the placement and height of propped fractures is proposed. Gd2O3 was incorporated into ceramic proppant and a Monte Carlo method was utilized to build the logging tools and formation models. Characteristic responses of the recorded information of different logging tools to fracture widths, proppant concentrations and influencing factors were studied. The results show that Gd capture gamma rays can be used to evaluate propped fractures and it has higher sensitivity to the change of fracture width and traceable proppant content compared with the exiting non-radioactive proppant evaluation techniques and only an after-fracture measurement is needed for the new method; The changes in gas saturation and borehole size have a great impact on determining propped fractures when compensated neutron and pulsed neutron capture tool are used. A field example is presented to validate the application of the new technique.}, journal={APPLIED RADIATION AND ISOTOPES}, author={Liu, Juntao and Zhang, Feng and Gardner, Robin P. and Hou, Guojing and Zhang, Quanying and Li, Hu}, year={2015}, month={Nov}, pages={139–143} }