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This study aims to predict the productivity of an open-hole horizontal gas well (OHHGW) in a gas reservoir with closed bottom and top boundaries (GRCBTBs). First, according to the theory of mirror imaging, an OHHGW in GRCBTBs is transformed into an infinite well array in infinite formation. Second, based on conformal transformation principle, the infinite well array is transformed into two production and two injection wells in the complex plane. Finally, according to the superposition principle of potential, a new productivity prediction method, which is suitable for the horizontal well in GRCBTBs, was developed. The field measured data of Jingbian gas field of Ordos Basin demonstrate the ability of the method to accurately predict the productivity of the OHHGW in GRCBTBs, and the prediction relative error of absolute open flow of well Longping 1 is only 1.03%, that is to say that the method proposed in this study has a certain guiding significance for the development of horizontal wells in GRCBTBs.

Based on analysis of NMR T2 spectral characteristics, a new method for identifying fluid properties by decomposing T2 spectrum through signal analysis has been proposed. Because T2 spectrum satisfies lognormal distribution on transverse relaxation time axis, the T2 spectrum can be decomposed into 2 to 5 independent component spectra by fitting the T2 spectrum with Gauss functions. By analyzing the free relaxation response characteristics of crude oil and formation water, the dynamic response characteristics of the core mutual drive between oil and water, the petrophysical significance of each component spectrum is clarified. T2 spectrum can be decomposed into clay bound water component spectrum, capillary bound fluid component spectrum, micropores fluid component spectrum and macropores fluid component spectrum. According to the nature of crude oil in the target area, the distribution range of T2 component spectral peaks of oil-bearing reservoir is 165–500 ms on T2 time axis. This range can be used to accurately identify fluid properties. This method has high adaptability in identifying complex oil and water layers in low porosity and permeability reservoirs.

This study aims to interpret the temperature and pressure behavior of an open-hole horizontal gas well (OHHGW) in a low-permeability gas reservoir in order to obtain the permeability and production profile of the OHHGW. First, the mathematical model, which is comprised of viscous dissipation, friction, the Joule–Thomson effect, and several other micro-thermal effects, was developed under a single-phase condition. Second, during the process of solving the numerical model, the drilling skin, heterogeneity, and non-Darcy effect were taken into consideration. In addition, the reservoir and wellbore models were coupled. Third, the testing temperature and pressure data were inverted using the Levenberg–Marquardt (LM) or Markov Chain simulated annealing algorithms, and the permeability and production profiles of the wellbore were obtained. The synthetic cases demonstrate the models’ ability to predict the temperature profile, and the results show the following: (a) The inversion results are in good agreement with the actual data, that is, the model can provide effective guidance for horizontal well development. (b) The wellbore temperature is lower than that of the reservoir boundary, so the micro-thermal effects for the horizontal gas well cannot be ignored during production. (c) As the gas production, the relative density of the gas, and the drilling skin factor increase, the wellbore temperature profile gradually decreases. The wellbore temperature increases with increasing horizontal permeability. (d) The trend of the temperature profile is contrary to the flow path of the wellbore fluid. (e) Reservoir heterogeneity has a significant influence on the temperature profile.