The Hu-12 Block, located in ZhongYuan Oilfield, Henan Province China, contains many small but highly heterogeneous oil reservoirs, with low permeability oil bearing formations and high permeability mixed (oil/water) layers. The reservoir temperature is 90 o C, and the original reservoir pressure of nearly 25 MPa, and with high salinity of formation water (around 200,000 mg/l). After 20 years of water injection, the recovery factor achieved was only 20-25%, and average water cut has reached to over 95%. N 2 gas injection has been tried with less success due to early gas breakthrough from high permeability zones. Since 2006, high pressure air foam and air injection (Air Foam Alternative Air Injection, AFAAI) has been proposed and implemented in one of the reservoirs, in order to block high permeability water zones and increase the sweeping efficiency of air and water injection. A series of laboratory experiments have been conducted to study the oxidation kinetics of air/air foam with oil and the blocking and displacement efficiency of air foams in different oil sands. Reservoir simulation has also been carried out for predicting the reservoir response to air foam injection and optimizing the injection process. Air foam and air injection was started in the field since May 2007 in a well group with 1 injector and 4 producers, using a small high pressure air compressor (40 MPa, 7 m 3 /min air rate). Up to now, 460,000 Nm 3 air and 2920 m 3 foam surfactant solution have been injected into the reservoir. The field results show that no oxygen/N 2 breakthrough was observed and a significant increase in oil production with water cut reduced by 4%. The detailed laboratory study and field experience are presented in this paper.

We use five published source models to calculate the Coulomb failure stress changes induced by the M s 8.0 Wenchuan earthquake, and analyze the association between stress changes and the subsequent earthquakes. Based on the analysis of uncertainties resulting from source models, we determine the stress changes on nearby faults caused by the Wenchuan earthquake. Moreover, we focus on the seismicity rate change as a function of time on every fault under the influence of stress changes. The results indicate that the spatial distributions of aftershocks correlate well with the regions where stress is calculated to increase using the related models. The largest lobes of dropped stress lie in the west and east sides of source fault. The largest lobes of increased failure stress close to southern and northern ends of the source fault extend into the whole source failure plane. In addition, another region of increased stress lies in the Wenchuan-Yingxiu zone close to the southern segment of source fault, where a large number of aftershocks have occurred. And subsequent earthquakes seem to extend to even more remote distances; therefore, this area also has a high risk of seismic hazard. We find that the positive stress changes on nearby faults imposed by the Wenchuan earthquake produce an encouraging effect on seismicity rate. The effect is most significant on the Pengxian-Guanxian fault and Qingchuan fault, the value of seismicity rate maintains two times greater than the value before the mainshock for the next hundred years on these faults, and the time needed for the aftershock rate to recover to the pre-mainshock seismicity rate can reach up to 800-900 yr. The influence is not significant on the western Qinling fault, the Longquanshan fault, the Xianshuihe fault, the Yulongxi fault, the Anninghe fault, the Minjiang fault, and the Aba fault. Compared with the seismicity rate on these faults before the mainshock, the aftershock rate is raised by less than two times, and the time of perturbation duration is not long. The stress changes on the Fubianhe fault and Huya fault are negative, which reduce the seismicity for the next thousand years. Under the influence of stress changes caused by the Wenchuan earthquake, both Pengxian-Guanxian fault and Qingchuan fault have a high risk of earthquake occurrence.Wenchuan earthquake, optimally oriented fault, Coulomb stress change, seismicity rate Citation:Xie C D, Zhu Y Q, Lei X L, et al. Pattern of stress change and its effect on seismicity rate caused by M s 8.0

XinJiang oilfield is located in the Northwest of China, in which large oil reserves have been discovered in reservoirs with very low permeability (<14×10 -3 μm 2 ). These reservoirs are featured with light oil in moderate depth, high reservoir pressure, but relatively low reservoir temperature (65~78 o C) and low oil viscosity (<10mPa•s). Primary production and limited water flooding experience have shown that the recovery factor in these reservoirs is very low due to lack of reservoir energy and poor water injectivity. Gas injection has been optioned as an alternative secondary or tertiary technique to maintain reservoir pressure and/or increase sweeping and displacement efficiency. In this study, the feasibility of air injection via a low temperature oxidation (LTO) process has been studied. Laboratory experiments were focused on LTO characteristics of oil samples at low temperature range and core flooding using air at various reservoir conditions. Reservoir simulation studies were conducted in order to predict the reservoir performance under the air injection scheme and to optimize the operational parameters. The oxygen consumption rates at reservoir temperature and IOR potentials at different reservoir conditions were assessed for a number of selected reservoirs in the region. A pilot project has been designed based on experimental data, reservoir simulation results and field experience of air injection gained in other regions of China. Issues related to safety and corrosion control during air injection and the project economics were also addressed in the paper.

CO 2 huff-n-puff is an effective technique used in shale-oil reservoirs for supplementing the formation energy and realizing efficient development. This study focuses on typical shale core samples and crude oil. The quantitative evaluation of CO 2 huff-n-puff recovery in shale-oil reservoirs at different pore scales was performed using the nuclear magnetic resonance technology combined with a laboratory physical simulation experiment. The huff-n-puff pressure and soaking time were considered as control variables. The results indicate a positive correlation between the oil recovery at different pore scales in a shale-oil reservoir and the CO 2 huff-n-puff pressure. The production degree for a smaller pore was larger in the range 0−12.0 MPa; further, the production degree for a larger pore gradually increased with the CO 2 huff-n-puff pressure. The soaking time had a considerable effect on the oil recovery at different pore scales. For a long soaking time (120 h), the production degree of crude oil in a large pore increased with the CO 2 huff-n-puff pressure. However, for a short soaking time (24 h), the low huff-npuff pressure stage (0−12.0 MPa) was dominated by the production of crude oil at a small pore scale, while the high huff-n-puff pressure stage (16.0−20.0 MPa) was dominated by the production at a large pore scale.

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