Study On Saturation Model And Log Interpretation Method Of Altered Volcanic Lava Rock Reservoirs

With the improvement of oil exploration technology and decreasing of conventional reservoirs, More and more unconventional reservoirs are getting attention. Volcano rock reservoirs are being the key content of research gradually. Volcanic lava rock reservoirs are unconventional reservoirs, whose pore types and structures are relatively simple and the mineral composition of rock is relatively stable. The original rocks are likely to suffer a series of secondary changes such as alteration, dissolution, leaching, filling. These secondary changes often bring some challenges to volcano logging evaluation.There is universal altered phenomenon in volcano lava rock reservoirs. So far, researchers have done lots of deeply study about mineral altering reasons, types and conditions. While, there is no comprehensive and systematic research to the altered volcanic reservoirs. Based on the research to mineral altered mechanism, the characteristics and the influences on logs from altering are researched in this paper. Saturation and evaluation equation are the focus content of this paper.The research object is the volcano lava rock reservoirs in the research area. This thesis studied the character of altered layer and unaltered layer of the same rock lithology in the same well though the rock sheet analysis data, and get the characters and changing lows of logs in alter volcano lava rock reservoirs. As a result, secondary changes often happen with dissolution and filling usually. Altering often enlarges the porosity and permeability of reservoirs, and filling makes a poor porosity and permeability. While the porosity and permeability of reservoirs are difficult to be judged if they are exit in rock at the same time.Two parameters are introduced to this paper, altering index is used to characterize the altering degree of rock and physical property index is used to characterize the physical property of rock. Both of them are used to evaluate the physical property of the altered reservoirs.A volume model includes three parts: skeleton minerals, pore and clay mineral. The volume of each part is calculated by density logging and compensated neutron logs. Based on the theory of connective conducting, the saturation equation including skeleton phase, matrix phase and clay phase is derived combining mix conduction law. The equation is reasonable in theory and considered the microscopic conductive effect. While calculating some parameters in the equation are difficult. The porosity indexes in equations are selected by experience. The disadvantages above bring some uncertainty to reservoir evaluation as well. According to the feature of altered volcano lava rocks reservoirs, Doll model in which conductivity of clay minerals is considered can be used to evaluation saturation in the reservoirs. The premise is that there are no cracks in the altered volcanic lava rocks reservoirs. The parameter optimized modal was used to research area and get a better result.The innovations of this paper are as follows:The effect of alteration on logging data of volcanic lava reservoirs was researched and alteration index and physical property index were used to evaluate the reservoirs.The total property and the clay mineral content was calculated through making single mineral neutron-density cross plot;According to the feature of altered volcano lava rocks reservoirs, Doll model in which conductivity of clay minerals is considered can be used to evaluation saturation in the reservoirs.