Development a Statistical Relationship between Compressional Wave Velocity and Petrophysical Properties from Logs Data for JERIBE Formation ASMARI Reservoir in FAUQI Oil Field

The Compressional-wave (Vp) data are useful for reservoir exploration, drilling operations, stimulation, hydraulic fracturing employment, and development plans for a specific reservoir. Due to the different nature and behavior of the influencing parameters, more complex nonlinearity exists for Vp modeling purposes. In this study, a statistical relationship between compressional wave velocity and petrophysical parameters was developed from wireline log data for Jeribe formation in Fauqi oil field south Est Iraq, which is studied using single and multiple linear regressions. The model concentrated on predicting compressional wave velocity from petrophysical parameters and any pair of shear waves velocity, porosity, density, and fluid saturation in carbonate rocks. A strong linear correlation between P-wave velocity and S-wave velocity and between P-wave velocity and density rock was found. The resulting linear equations can be used to estimate P-wave velocity from the S-wave velocity in the case of both. The results of multiple regression analysis indicated that the density, porosity, water-saturated, and shear wave velocity (VS) are strongly related to Vp.

Understanding how overpressure affects the physical properties of sandstones

Overpressure is one of the major difficulties we have to face when exploring the deep earth. Geophysical remote sensing methods, especially seismic and electrical methods, are widely employed to predict overpressure for de-risking the drilling of deep boreholes in the earth’s crust. However, there are major uncertainties in relating the measured geophysical parameters to the physical properties of crustal rocks, needed for reliable overpressure estimation. We address this knowledge gap through dedicated laboratory measurements of elastic velocity, electrical conductivity and porosity with increasing pore pressure and the analyses and interpretation of the experimental results. We find a linear increase in the porosity, and an exponential increase and decrease in the electrical conductivity and compressional wave velocity, respectively with increasing pore pressure. We also find an exponential reduction in the cementation exponent and effective pore aspect ratio inverted from the pore pressure induced electrical conductivity and compressional wave velocity, respectively. We further demonstrate that the changing cementation exponent and effective pore aspect ratio by increasing pore pressure affects more significantly the electrical and elastic rock properties than does by dilating porosity. The results not only strengthen our understanding of the influencing mechanism of overpressure on the physical properties of crustal rocks, but also provide new insights for the more reliable detection of overpressure zones from geophysical remote sensing.

THE LITHOSTRATIGRAPHY OF THE NEAR-SURFACE IN PART OF SEDIMENTARY KOLMANI FIELD IN NORTHERN BENUE TROUGH, NIGERIA, USING SOIL CORE AND SEISMIC REFRACTION DATA

Soil samples from 31 shallow boreholes were acquired at depths 0m, 1m, 2m, 3m, 4m, 5m, 7m, 10m, 15m, 20m, 25m, 30m, 35m, 40m, 45m, 50m, 55m, and 60m in Pingida (Kolmani Field) in Ako LGA, Gombe State, Nigeria. Using the same boreholes, seismic refraction data was also acquired. The aim of the survey was to delineate the near-surface lithology and velocity layering. The boreholes were drilled using rotary drilling rig and the core samples acquired and described using Wentworth Scale. Seismic refraction data acquired using a single trace Stratavisor NZXP portable digital recorder. The recording spread consisted of a single SM4- 10Hz geophone positioned at depths where the soil samples were taken. A hammer was used as the energy source and placed 3m away from the hole to obtain the first breaks. The refraction data was interpreted using UDISYS Version 1.0.0.0 software. The soil layers in the Kolmani Field have three distinct layers specified as follows, namely, top weathered and sub-consolidated layers made up of intercalation of sandstone, gravel ash clay and muddy coal shale. The lithologic strata do not correlate throughout the field resulting from the highly variable elevation which ranged from 317m and 524m with average of 389.16m. The top weathered layer of laterite intercalated with cobblestones with compressional wave velocity ranging from 342 ms-1 to 517 ms-1 with an average of 405.03 ms-1. Beneath the weathered layer is the sub-consolidated Clay layer intercalated with silt and laterite of compressional wave velocity ranging from 440 ms-1 to 1854 ms-1 of average of 826 ms-1. The underlying consolidated layer is the shale and coal layer having compressional wave velocity ranging from 1518 ms-1 to 4201 ms-1 with an average of 2162.65 ms-1. The dominant lithologic sequences encountered are laterite, clay, silt, sand, gravel, coal and shale. The results of this work can be used for static corrections in seismic reflection processing, planning and assessing risk for engineering structures, and for groundwater exploration. The laterite, clay, silt, sand, gravel, coal and shale can be utilized in agriculture, construction, process industries, and environmental remediation.

Predicting Unconfined Compressive Strength Decrease of Carbonate Building Materials against Frost Attack Using Nondestructive Physical Tests

Carbonate building materials and engineering constructions are exposed to severe seasonal environmental fluctuations and result in a full or partial disintegration, especially in cold regions, and employment of nondestructive methods for evaluating the durability of building materials subject to frost weathering is gaining great significance. This research aims to obtain reliable relationships between unconfined compressive strength decrease and nondestructive parameters variations of limestone types under frost conditions and provide useful information regarding their durability in order to ensure the long-term viability or sustainability of these materials used for constructions against frost conditions. In this study, five important types of Chinese limestone used as construction materials were subjected to 50 frost cycles. Unconfined compressive strength, compressional wave velocity and spatial attenuation, and porosity were obtained at the end of every 10 cycles. As a result of progression in frost cycles, the increase and decrease rates were determined at the end of every 10 cycles, and the relationships between them were obtained to predict the loss ratios of unconfined compressive strength (RDσc). Results indicated that at the end of 40th cycles, there was a high correlation between RDσc and spatial attenuation loss with an R2 of 0.8584. Furthermore, there was also a strong relationship between RDσc and compressional wave velocity decrease after the end of 20th and 50th cycles with an R2 of 0.9089 and 0.9025, respectively. Therefore, these relations are reliable to provide useful information for durability and viability of studied samples under frost conditions and support the use of the ultrasonic measurements. It can also be successfully used for pre-estimation of unconfined compressive strength loss of studied limestone types against frost weathering without any tests.