Cumulative Gas Production Rate Research Articles

Effect of pressure drawdown rate on the fluid production behaviour from methane hydrate-bearing sediments

Methane hydrates have been considered as the future source of energy due to its vast resource volume and high energy density. Depressurization has been demonstrated to be a technical feasible method in producing gas from hydrate reservoirs in the past field production tests. However, major technical challenges, i.e. low gas production rate, excessive water production, and uncontrollable sand production remain. Such undesirable production behaviour is directly linked to one key process variable, the rate of pressure drawdown. It controls the rate of hydrate dissociation and governs the multiphase fluid flow in sandy media. However, precise control of bottom hole pressure in large-scale production tests is difficult and it remains unclear how different drawdown rates affect the fluid production behaviour. Herein, we performed a series of hydrate formation experiments synthesizing aqueous-rich methane hydrate-bearing sediments with hydrate saturation above 40% and subsequently a series of depressurization experiments employing different controlled drawdown rates to dissociate the hydrate-bearing samples. Cumulative production of gas and water were monitored during the depressurization. The goals of the experiments were to examine the fluid production rate, the recovery ratio, and the temperature response in the hydrate-bearing system under different drawdown strategies. Cumulative water production rate increases linearly with drawdown rate, while cumulative gas production rate is directly linked to the hydrate dissociation rate, which is controlled by heat transfer at the early stage and dissociation kinetics toward the final stage. Water gas ratio can be regulated within a threshold by employing a slow drawdown rate. In addition, the final recovery of fluid is not controlled by the drawdown rates but is related to the final stable conditions of pressure and temperature. Our findings expand the understanding of fluid production behaviour from hydrate-bearing sediments and provide guidance in optimizing production strategies and in assessing the fluid production potential for future experiments and field production tests from hydrate reservoirs.

Transport feasibility of proppant by supercritical carbon dioxide fracturing in reservoir fractures

The pure supercritical carbon dioxide (SC-CO2) fracturing prevents the clay from swelling and avoids the water lock as compared with the slick-water fracturing. The CO2 molecule could replace the CH4 adsorbed in organic matter and tiny particles on the clay mineral surface in the formation. This leads to an increased cumulative gas production rate. The SC-CO2 fracturing is an alternative waterless fracturing technique for an effective future development of shale gas reservoirs. Due to its low density and viscosity as compared with the slick-water, it attracts attentions for the proppant transport. In this paper, the two phase flow of the SC-CO2 and the proppant in fractures during the SC-CO2 fracturing is analyzed with the computational fluid dynamics method. The characteristics of the proppant transport by the SC-CO2 fracturing and the slick-water fracturing are compared. Moreover, a sensitivity analysis is also performed to see the influence of various parameters on the proppant transport ability of the SC-CO2 fracturing. It is shown that the proppants in the SC-CO2 and the slick-water have similar distribution characteristics. Reducing the proppant density, the proppant diameter, and the solid volume fraction as well as increasing the injection rate can all have similar filling effects on the fractures. The feasibility of the proppant transport by the SC-CO2 fracturing in fractures is revealed and a guidance is provided for the SC-CO2 fracturing design.

Numerical simulation and field application of diverting acid acidizing in the Lower Cambrian Longwangmiao Fm gas reservoirs in the Sichuan Basin

The Lower Cambrian Longwangmiao dolomite gas reservoirs in the Sichuan Basin are characterized by well-developed natural micro-fractures and dissolved pores and cavities. Due to the strong heterogeneity of reservoirs and the serious damage of drilling and completion fluids, acid placement is difficult, and especially the acidizing stimulation of long-interval highly deviated wells or horizontal wells is more difficult. In this paper, the diverting mechanism and rheological behavior of viscoelastic surfactant (VES) based diverting acid was firstly investigated, and the diverting acid with good diversion performance and low secondary damage was selected as the main acid. Then, based on the experimental results of its rheological behaviors, an empirical model of effective viscosity was fitted and a two-scale wormhole propagation model was coupled. And accordingly, a mathematical model for the acidizing of self-diverting acid was established to simulate the pH value, Ca2+ concentration, effective viscosity and wormhole shape under the effect of diverting acid in long-interval highly deviated wells that are non-uniformly damaged. Finally, gelled acid and 5% VES diverting acid were compared in terms of their etched wormhole shapes, flow rate distribution and acid imbibition profiles. It is shown that the diverting acid can obviously improve the acid imbibition profile of strong-heterogeneity reservoirs to intensify low-permeability reservoir stimulation. In view of the strong heterogeneity of Longwangmiao dolomite reservoirs and the complexities of drilling and completion fluid damage in the Sichuan Basin, a placement technology was developed for variable VES concentration diverting acid in horizontal wells and long-interval highly deviated wells completed with slotted liners. This acid placement technology has been practically applied in 8 wells and their cumulative gas production rate tested at the wellhead is 1233.46 × 104 m3/d. The average production stimulation ratio per well is up to 1.95. It provides a support for the efficient development of the Longwangmiao giant gas reservoir.

Influences of Surfactant Tween 80 on the Gas Production, Cellulose Digestion and Enzyme Activities by Mixed Rumen Microorganisms

The surfactant Tween 80 was evaluated for its ability to influence cumulative gas production, cellulose digestion, and enzyme activities by mixed ruminal microorganisms grown on barley grain or Orchardgrass hay. The addition of Tween 80 at a level of 0.10% significantly (p<0.05) decreased the cumulative gas production rate from both barley grain or Orchardgrass hay substrates. However, 0.05% Tween 80 did not affect gas production rates compared to the control treatment. The addition of 0.05% Tween 80 to cultures growing on barley grain resulted in a significant increase in cellulase (90.01%), xylanase (90.73%) and amylase (487.25%) activities after 30 h incubation. Cultures utilizing Orchardgrass hay had a significant increase in cellulase (124.43%), xylanase (108.86%) and amylase (271.22%) activities after 72 h incubation. These increases in activities were also observed with cultures supplemented with 0.10% Tween 80 throughout all the incubation times tested. These results indicated that the addition of 0.05% Tween 80 could greatly stimulate the release of some of key enzymes without decreasing cell growth rate in contrast to trends reported with aerobic microorganism. Our data indicates potential uses of the surfactant Tween 80 as a feed additive for ruminant animals. (Asian- Aust. J. Anim. Sci. 2003. Vol 16, No. 8 : 1151-1157)

Methanogenesis of water hyacinth in the presence of boron compounds

Cowdung, human excreta, distillery effluents etc. are used for biogas generation in India. The addition of various boron compounds at different concentrations was made to study its effect on the cumulative gas production rate. A retention time of 15 days in a small batch digester was used. Additions of borax, boron hydride, boric and borozol were made at appropriate levels. The addition of such compounds affected the methanogenesis and increased gas generation.