Peng Pei

Cost comparison of syngas production from natural gas conversion and underground coal gasification

Underground coal gasification (UCG) is a promising technology to reduce the cost of producing syngas from coal. Coal is gasified in place, which may make it safer, cleaner and less expensive than using a surface gasifier. UCG provides an efficient approach to mitigate the tension between supplying energy and ensuring sustainable development. However, the coal gasification industry presently is facing competition from the low price of natural gas. The technology needs to be reviewed to assess its competiveness. In this paper, the production cost of syngas from an imaginary commercial-scale UCG plant was broken down and calculated. The produced syngas was assumed to be used as feedstock in liquid fuel production through the Fischer-Tropsch process or methanol synthesis. The syngas had a hydrogen (H2) to carbon monoxide (CO) ratio of 2. On this basis, its cost was compared with the cost of syngas produced from natural gas. The results indicated that the production cost of syngas from natural gas is mainly determined by the price of natural gas, and varied from

A rigorous method to calculate the rising speed of gas kick

24.46 per thousand cubic meters (TCM) to

Shale gas reservoir treatment by a CO2-based technology

90.09/TCM, depending on the assumed price range of natural gas. The cost of producing UCG syngas is affected by the coal seam depth and thickness. Using the Harmon lignite bed in North Dakota, USA, as an example, the cost of producing syngas through UCG was between

Waste heat recovery in CO2 compression

37.27/TCM and

Thermodynamic impact of aquifer permeability on the performance of a compressed air energy storage plant

39.80/TCM. Therefore, the cost of UCG syngas was within the cost range of syngas produced by natural gas conversion. A sensitivity analysis was conducted to investigate how the cost varies with coal depth and thickness. It was found that by utilizing thicker coal seams, syngas production per cavity can be increased, and the number of new wells drilled per year can be reduced, therefore improving the economics of UCG. Results of this study indicate the competitiveness of UCG regarding to natural gas conversion technologies, and can be used to guide UCG site selection and to optimize the operation strategy.

Determining the permeability of tight rock with gas transient flow

The rising speed of gas kick is an important parameter in well control operation. The position of the gas kick dictates the pressure at the casing shoe, which is usually the weakest point in the openhole section, and the wellhead pressure, which is one of the key factors affecting the blowout preventer and choke folder. In this research, we derived a rigorous model to estimate the rising speed of gas kick. Starting from the force analysis and mass conservation, we developed equations to calculate the forces exerting on the gas kick. With the mass of the gas kick, the rising speed of the gas kick is calculated. The effect of wellbore temperature profile on the rising of the gas kick is taken into account in the derivation. Before the development of this model, the estimation of gas kick position is commonly based on experience. In many cases, the experience alone is not good enough for well control. The proposed model provides a new approach with solid theoretical base to characterize the rising of gas kick in the hole. It makes the procedure of the well control simple and makes drilling engineers feel more comfortable to control the well. The new model can be combined with engineers experience to predict the downhole situation, shut-in casing pressure, and mud rate as a functions of position of gas kick. Any deviation from the forecast indicates accidents or downhole problems. Therefore, the proposed model is a valuable tool to diagnose the problems in well control.