Tuff Reservoir Research Articles

春风油田石炭系开发技术研究

针对准噶尔盆地春风油田石炭系已落实规模储量但试采产能差异较大的情况，开展了实用开发技术研究。发现，春风油田石炭系储层岩性均为火山岩，以孔隙–裂缝性储层、普通稠油为主。排61等6口井火山凝灰岩储层常规试采均获得工业油流，且保持了持续稳定生产。其中，排66井生产井段岩性为灰色油斑火山凝灰岩，已连续生产652 d，累计产油量7099 t，50℃脱气原油黏度154 mPa∙s。排666和排681井火山角砾岩储层水力喷砂压裂获得工业油流。基于石炭系储层在春风油田发育广泛且比较稳定，发育连续型大型地层油藏的可能性很大，部署的第一口水平井排664侧井成功钻遇水平段486 m，已获得工业油流。According to Chunfeng Oilfield Carboniferous in Junggar Basin with volumes of reserves, while there is a productivity of great difference by production test, a practical development technology study is launched. It is shown that reservoir lithology of Chunfeng Oilfield Carboniferous is volcanic rocks, which is mainly pore-fracture type reservoir and ordinary heavy oil. Industrial oil flow is obtained by normal producing of volcanic tuff reservoir of 6 wells (e.g. Pai61 Well), and the yield is stable. Pai66 Well whose producing interval is grey oil spot volcanic tuff has produced for 652 d continuously, having cumulative oil production of 7099 t; and the oil viscosity is 154 mPa∙s at 50˚C. Industrial oil flow of hydraulic sand blast fracturing is obtained in the volcanic breccias reservoir of Pai666 and Pai681 Well. Based on the wide and stable development in the Carboniferous reserves of Chunfeng Oilfield, the development of continuous large-size stratigraphic oil pool is more possible. The first horizontal well (Pai664C) has successfully drilled to the horizontal section of 486 m, obtaining industrial oil flow.

火山岩孔隙–裂缝型储层特征与渗流叠加效应——以准噶尔盆地西缘排66地区为例

春风油田位于准噶尔盆地西缘，17口探井钻遇孔隙–裂缝型火山岩油藏，其中4口探井获得了工业油流，为扩大勘探成果，开展了高产机理研究。研究发现，春风油田石炭系火山岩高产有利条件为：储层为火山凝灰岩，岩心含油级别为油斑级，储层裂缝发育，地下原油黏度较低。在分析高产原因的过程中，发现了孔隙–裂缝渗流叠加效应。即孔隙–裂缝沟通后，产生了由于优于单纯孔隙型储层或单纯裂缝型储层的开发效果。孔隙–裂缝叠加渗透率是测井解释储层渗透率的多倍，为采用水平井和长井段压裂提供了理论依据。 Chunfeng Oilfield was located in the West Edge of Junggar Basin, with 17 exploratory wells drilled in pore- fracture type reservoirs of Volcanic Rock, among which 4 exploratory wells obtained industrial oil flow. To expand exploration results, high yield mechanism research is developed. Research shows that, the advantages for high yield conditions of Volcanic Rock in Chunfeng Oilfield are: volcanic tuff reservoir, core oil grade with oil spot, reservoir fractures and lower underground oil viscosity. In this process, pore-fracture seepage additive effect has been discovered. Pore-fracture produced better development effect than both simple pore and fracture. Pore-fracture additive permeability is many times the log interpretation permeability, and it provides theoretical basis for horizontal well and long channel fracturing.

南長岡ガス田における断裂分布の予測 応力分布および岩石物性変化からみた断裂の発達様式

In the Minami Nagaoka gas field, north-northeast to south-southwest trending break-out dominate. The trend of maximum horizontal stress is vertically crossing the break-out that means west-northwest to east-southeast. The minimum horizontal stress value estimated from hydraulic fracturing method is slightly smaller than overburden pressure. The maximum horizontal stress is 1.58 times larger than the minimum horizontal stress. The Green Tuff in this field is expected to be in a strike-slip faulting regime, and the estimated differential stress at the depth of 4, 300m is about 490ksc. The Green Tuff exposed to tectonic stress largely exceeding the horizontal stress of a standard overburden pressure state. Therefore the dominant trend of opening fractures is assessed to be controlled by subsurface stress and to be parallel to the maximum horizontal stress.The results of triaxial compression test show that different lithofacies exhibit different stress-strain profile. This implies that the Green Tuff has the inner stress distribution controlled by lithological variation. Therefore, it is highly possible that the difference in deformation behavior, such as brittleness or ductility of the lithofacies in reservoir creates the environment in which remnant stress and local opening fractures are maintained in the Green Tuff reservoir.The combination of the regional tectonic stress and local stress distribution caused by lithofacies's variation is likely to control the distribution of opening fractures and therefore quality of the Green Tuff reservoir.

Reservoir processes and fluid origins in the Baca Geothermal System, Valles Caldera, New Mexico

At the Baca geothermal field in the Valles caldera, New Mexico, 19 deep wells were drilled in an attempt to develop a 50‐MWe (megawatts electric) power plant. The chemical and isotopic compositions of steam and water samples have been used to indicate uniquely the origin of reservoir fluids and natural reservoir processes. Two distinct reservoir fluids exist at Baca. These fluids originate from the same deep, high‐temperature (335°C), saline (2500 mg/kg Cl) parent water but have had different histories during upflow. One fluid (from wells 4 and 13) is isotopically light, high in radiogenic noble gases, CO2 and HCO3, and low in Ca. It has a temperature of 290°–295°C and a reservoir chloride near 1900 mg/kg. This fluid resulted from rapid upward flow through 1.1‐ to 1.4‐m.y.‐old Bandelier Tuff reservoir rocks after long residence in pre‐Bandelier (>7 m.y.) sediments and Precambrian basement rocks and 25% dilution with high‐altitude cold groundwater from Redondo Peak. The other water (from wells 15, 19, and 24) moved slowly through the Bandelier Tuff and cooled conductively (with minor steam loss for well 19) from 335°C to 280°–260°C. Apparently, short residence in old basement rocks has left this water with low radiogenic gases. Conductive cooling without mixing has kept the original chloride and relatively heavy isotope composition of the deep water. The recharge to the deep parent water is not well understood but may be from lower elevation precipitation outside the Valles caldera area. Gases are in equilibrium in all‐liquid reservoir fluids at near reservoir temperatures, and the concentrations of atmospheric gases are similar to those of air‐saturated water, indicating little boiling and steam loss. All water, solutes, and gases in the reservoir fluids originate from air‐saturated meteoric recharge water, watermineral reactions, and rock leaching, with the possible exception of excess 3He that must have an ultimate mantle source. This gas could originate directly from magma or from leaching of intrusive volcanic rocks beneath the Bandelier.

Applications of Hydrochloric Acid to Vitric Tuff Reservoirs

Vitric tuff is the most common reservoir rock in Akita. Fujioka and Yoshikawa recently suggested that the permeability of vitric tuff decreased when the tuff reacted with high alkali drilling mud under well conditions. They also said that oil wells producing oil from such a reservoir were required to be stimulated by acidizing treatment. Our purpose here is to investigate the reactions of hydrochloric acid on vitric tuff. The vitric tuffs used in these experiments were from 10 per cent to 20 per cent soluble when the pulverized samples were immersed in HCL at 30°C for 24 hours. The permeability of the vitric tuffs was measured with the apparatus shown in Fig. 4. Hydrochrolic acid and 1.5 per cent NaCl solution were used in the flow tests. The results are shown in Fig. 6 and Fig. 7.