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-CoalBed Methane (CBM), as one kind of unconventional gas, is an important energy resource, attracting industry interest in research and development. Using the Langmuir adsorption isotherm, Fick's law in the matrix and Darcy flow in cleat fractures, and treating the Stimulated Reservoir Volume (SRV) induced by hydraulic fracturing as a radial composite model, the continuous linear source function with constant production is derived by the methods of the Laplace transform and Duhamel theory. Based on the linear source function, semi-analytical solutions are obtained for a fractured vertical well producing at a constant production rate or constant bottom-hole pressure. With the help of the Stehfest numerical algorithm and computer programing, the well test and rate decline type curves are obtained, and the key flow regimes of fractured CBM wells are: wellbore storage, linear flow in SRV region, diffusion flow and later pseudo-radial flow. Finally, we analyze the effect of various parameters, such as the Langmuir volume, radius and permeability in the SRV region, on the production performance. The research results concluded in this paper have significant importance in terms of the development, well test interpretations and production performance analysis of unconventional gas.Re´sume´-Analyse des performances de puits fracture´s avec un volume de re´servoir stimule´dans des gisements de charbon -Le gaz de houille (CoalBed Methane, CBM), en tant que gaz non conventionnel, est une ressource d'e´nergie importante, qui attire l'inte´reˆt industriel en matie`re de recherche et de de´veloppement. En utilisant l'isotherme d'adsorption de Langmuir, la loi de Fick dans la matrice et le flux de Darcy dans les fractures clive´es, et en traitant le volume de re´servoir stimule´(Stimulated Reservoir Volume, SRV) induit par la fracture hydraulique comme un mode`le composite radial, la fonction de source line´aire continue avec une production constante est obtenue par les me´thodes de la transforme´e de Laplace et de la the´orie de Duhamel. Sur la base de la fonction de source line´aire, des solutions semianalytiques sont obtenues pour un puits vertical fracture´produisant a`un taux de production constant ou a`une pression de fond constante. En s'aidant de l'algorithme nume´rique de Stehfest et de la programmation informatique, des courbes de test de puits et de de´clin de taux de production sont obtenues, et les re´gimes d'e´coulement cle´s des puits CBM fracture´s sont les suivants : stockage de puits de forage, flux line´aire dans la zone SRV, flux de diffusion et flux pseudo-radial ulte´rieur. Enfin, nous analysons l'effet de diffe´rents parame`tres, tels que le This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.Oil & Gas Science and Technology -Rev. IFP Energies nouvelles (2016) 71, 8 Ó Z. Yu-long e...

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Though polymer flooding is widely considered as a good EOR method for heterogeneous fields, it's always a difficulty to be applied in high temperature and high salinity reservoirs, limited by polymer property. GS-E31 reservoir in West China has ultra-high temperature, 258.8°F (126°C), and ultra-high salinity, 18×104mg/L. It is highly heterogeneous, developed with flowing channels. Starting in July 2012, a new polymer (SMG) flooding was pilot tested, with success technically and economically. Before SMG injection, tracer test was conducted in the pilot, figuring out the distribution position and direction of prevailing flowing channels. The microscopic pore structure and size were studied. The temperature and salinity resistance of the new particle-type polymer under reservoir condition was tested. The oil displacing effect was simulated on parallel dual core model. For the pilot test, two slugs with different particle sizes were designed. To guarantee the flooding effect, a preposed PPG (preformed particle gel) slug with larger size was designed to inhibit prevailing flow channels. The lab studies showed the new polymer particles kept stable appearance within 100 days under the reservoir temperature and salinity, denoting high capacity of temperature and salinity resistance. And by physical simulation it could obtain EOR of 12.3%. The pilot test was started in July 2012 and ended in December 2013, and the total liquid injection amount was 12.2×104m3, which was 0.1 PV. During operation, the polymer particle size and concentration were adjusted based on the observing data. As a result, the monthly oil rate of the pilot was increased from 1313 t to 2049.6 t, with increase of 736.6 t; and the water cut was decreased from 91.7% to 84.1%. The cumulative oil incremental was 1.03×104t, and the cumulative water production decrease was 4.79×104m3. The input-output ratio was 1:2.09. Though the economical result was not ideal, it was still acceptable under such severe reservoir conditions. Besides, the surveillance showed the preposed channeling inhibition slug did not perform well, which affected the NPF effect, and especially led to the quick water cut rising in the follow-up water injection phase. Summarizing the lat studies and pilot tests, the new particle-type polymer has obtained a large breakthrough for temperature and salinity resistance comparing to traditional polymer, and the EOR mechanism is different. The matching relationship between particle size and formation pore size is very important for polymer flooding effect. To further study on lab evaluation method and plan optimization is needed. The technology has important referencing meaning for efficiently developing high temperature and high salinity fields.

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The calculation of fluctuating pressure is necessary during the progress of trip in the managed pressure drilling, because the bottomhole pressure should be constant during the progress of trip. The prediction model of the fluctuating pressure during the progress of trip was established based on the unsteady flowing theory. The actual application state of the prediction model was presented through a computational example. By the comparison between the computational result and the field test result, the computational result matches the field test result very well, which indicates the rationality and the accuracy of the model.

Drilling fluid density is very sensitive to the variation of temperature and pressure, especially in deep water and high temperature/high pressure environment. As downhole environment is different from the environment at surface, there must be a difference of density under these two conditions. The accuracy of downhole density calculation is directly related to whether the true downhole hydrostatic pressure could be reflected or not. Drilling fluid could be compressed under high pressure as well as be expanded under high temperature conditions. This paper proposes two important relational equations based on isothermal compressibility and isobaric expansivity. One equation is the relationship between isothermal compressibility and pressure. In this case fluid's volumetric reduction under certain pressure increment could be obtained. The other equation is the relationship between isobaric expansivity and temperature. Similarly, fluid's volumetric increment with the increasing temperature could be gotten by this equation. Therefore the true hydrostatic pressure at downhole could be accurately described by solving these two equations. Experiment data results show that curves of isothermal compressibility with pressure and isobaric expansivity with temperature are both conformed to exponential form. Besides, there is a special set of temperature and pressure for a given drilling fluid. Under this special situation, the compressibility are exactly offset by thermal expansivity, then mud density remain unchanged. Field applications indicates that this density model can describe downhole hydrostatic pressure well at Northwest China and South China Sea. Through adjusting mud density by this model, the headache problem of shallow narrow mud density window formation at South China Sea is well overcome. In addition, the true downhole equivalent static density (ESD) is smaller than fluid density measured at surface in a HP/HT well of Northwest China, whereas the situation is just the opposite in a deepwater well at South China Sea. Undoubtedly, the analysis of downhole hydrostatic pressure is a key process in drilling engineering operations. Too often, failure to accurately monitor wellbore ESD can lead to high risk activities, such as excessive well costs and unscheduled trouble time. Consequently, the HT/HP density model proposed in this paper, which provides an effective way to deal with those problems, is worth applying and promoting.

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