Using artificial intelligence methods for shear travel time prediction: A case study of Facha member, Sirte basin, Libya

Shear wave travel time logs are major acoustic logs used for direct estimation of the mechanical properties of rocks. They are also important for prediction of critical drawdown pressure of the reservoir. However, core samples are sometimes not available for direct laboratory measurements, and the time-consuming dipole shear imager tool is generally not used. Hence, there is a need for simple indirect techniques that can be used reliably. In this study, cross-plots between the available measured shear travel time and compressional travel time from three oil wells were used, and three artificial intelligence tools (fuzzy logic, multiple linear regression and neural networks) were applied to predict the shear travel time of Facha member (Gir Formation, Lower Eocene) in Sirte Basin, Libya. The predicted times were compared to those obtained by the equation of Brocher. The basic wireline data (gamma ray, neutron porosity, bulk density and compression travel time) of five oil wells were used. Based on principle component analysis, two wireline data sets were chosen to build intelligent models for the prediction of shear travel time. Limestone, dolomite, dolomitic limestone and anhydrite are the main lithofacies in the Facha member, with an average thickness of about 66 m. The simple equation gave 87% goodness of fit, which is considered comparable to the measured shear travel time logs. The Brocher equation yielded adequate results, of which the most accurate was for the Facha member in the eastern part of the Sirte basin. On the other hand, the three intelligent tools’ predictions of shear travel time conformed with the measured log, except in the eastern area of the basin.

Exploration of Hidden Hydrocarbons in Old Wells Magid Field - Sirte Basin, Libya

It is increasingly important to improve field productivity in today's competitive market. One way to achieve this, is to add new wells which are expensive and time consuming. The other alternative is to identify bypassed hydrocarbons, track changes in saturations and detect movement of reservoir fluid contacts from existing well bores already in place. It is considerably more cost effective and often more environmentally friendly to explore for those hidden hydrocarbons in old wells rather than drill new wells. As the field matures, there is a need to reevaluate the formation in older reservoirs and to focus the development strategy and approach on bypassed oil pockets and depletion levels in producing intervals. The ability to acquire essential logging data behind casing adds a new dimension to cased hole formation evaluation for locating and evaluating potential hydrocarbon zones in a mature field as in Magid field. A basic petrophysical evaluation was performed incorporating the data recorded behind casing by applying {Cased Hole Formation Resistivity Logging (CHFRL)} in each of these wells. Based on the analysis of cased hole formation evaluation results. The un-depleted intervals were commercially exploited adding reserve to the asset. Keywards: Hydrocarbon zones, Majid Field, Sirte Basin, Libya, CHFRL

Delineation of Carbonate Buildups Using Advanced Seismic Attributes, NW Sirte Basin, Libya

The Paleocene reservoir formations of the Northwest Sirte Basin in North-central, Libya contains chaotic and mound-shaped seismic geometries that may have an impact on the performance of the reservoirs. It is crucial to characterize and interpret these complex geometries for future field development. Therefore, this study was utilized numerous seismic attributes to characterize and enhance the interpretation of the chaotic and mounded geometries. Data conditioning represented by spectral whitening and median filter was first applied to enhance the quality of the seismic data and remove random noise resulted from data acquisition and processing. It provided high-resolution seismic data and better-displayed edges and sedimentological features. Variance, root mean square (RMS), curvature, and envelope attributes were computed from the post-stack 3D seismic data to better visualize and interpret the chaotic and mound-like seismic geometries. Based on the seismic attribute analysis, the chaotic facies were interpreted as barrier reefs forming the margins of an isolated carbonate platform, whereas the small-scale mound-shaped facies was interpreted as patch reefs developed on the platform interior. Data conditioning methods and seismic attribute analysis that were applied to the 3-D seismic data have effectively improved the detection and interpretation of the chaotic and mounded facies in the study area. Keywords: Carbonate buildup, data conditioning, seismic attributes, Sirte Basin, Libya

3D Geological Model Creates Potential for Increased Production in Libyan Field

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 201417, “Reservoir Characterization and Geostatistical Model of the Cretaceous and Cambrian-Ordovician Reservoir Intervals, Meghil Field, Sirte Basin, Libya,” by Mohamed Masoud, Sirte Oil Company; W. Scott Meddaugh, SPE, Midwestern State University; and Masud Eljaroshi Masud, Sirte Oil Company, prepared for the 2020 SPE Annual Technical Conference and Exhibition, originally scheduled to be held in Denver, Colorado, 5–7 October. The paper has not been peer reviewed. The study outlined in the complete paper focuses on developing models of the Upper Cretaceous Waha carbonate and Bahi sandstone reservoirs and the Cambrian-Ordovician Gargaf sandstone reservoir in the Meghil field, Sirte Basin, Libya. The objective of this study is to develop a representative geostatistically based 3D model that preserves geological elements and eliminates uncertainty of reservoir properties and volumetric estimates. This study demonstrates the potential for significant additional hydrocarbon production from the Meghil field and the effect of heterogeneity on well placement and spacing. Introduction The reservoir of interest consists of three stratigraphic layers of different ages: the Waha and Bahi Formations and the Gargaf Group intersecting the Meghil field. The Waha reservoir is a porous limestone that forms a single reservoir with underlying Upper Cretaceous Bahi sandstone and Cambro-Ordovician Gargaf Group quartzitic sandstone. The Waha provides excel-lent reservoir characteristics. The Bahi has fair to good reservoir characteristics, while the Gargaf Group has very poor reservoir quality. The Waha and Bahi contain significant amounts of hydrocarbons. The Bahi is composed of erratically distributed detritus from the eroded Gargaf Group. The characteristic of the Gargaf sediments is quartzitic sandstones indurate to a quartzite with low reservoir quality.

SEISMIC ATTRIBUTES AIDED DETECTION OF NW-SE TRENDING FAULTS DEVELOPED ON AN ISOLATED CARBONATE PLATFORM IN THE NW SIRTE BASIN, NORTH CENTRAL LIBYA

The lower and upper Paleocene reservoir formations, the primary producing formations in the northwest Sirte Basin, north-central Libya have complex structures which have an impact on the performance of the reservoirs. It is extremely crucial to understand the complex relationships between the fault networks and stratigraphy of the area for future field development. However, delineating faults particularly subtle faults is not an easy process due to the low signal-to-noise ratio in the post stack seismic data despite the effort and careful process of the pre-stack data. Seismic attributes are critical tools in detecting and enhancing major and minor fault interpretation beyond the seismic resolution of the conventional seismic dataset. This study utilizes variance, root mean square, and curvature attributes computed from the post-stack 3D seismic data acquired in the northwest Sirte Basin to detect major and minor faults along an isolated carbonate platform. A spectral whitening and median filter were applied to improve the quality of the data and remove random noise resulted from data acquisition and processing steps. Those methods were utilized to provide high-resolution seismic data and better show edges and structural features. Numerous faults have been detected in the study area. Most major faults in the lower and upper Paleocene reservoir formations are located along the margins of the isolated carbonate platform and have a NW-SE trend. Data conditioning and seismic attribute analyses applied on the 3-D seismic dataset effectively enhanced our understanding of the reservoir complexity and improve the detection of the major and minor faults and fracture zones in the study area.

IS will retain a small but potent presence in Libya

Significance Weakened and dispersed since it was driven from its stronghold in Sirte in late 2016, IS has struggled to reassert itself, though it remains capable of carrying out attacks. Impacts Key state institutions in Tripoli will remain vulnerable to attacks by IS sleeper cells, as in late 2018. IS militants are likely to launch new attacks on energy infrastructure, particularly around the Sirte Basin and in Fezzan. IS's presence in Libya -- and its potential to exploit political power struggles -- will further deter foreign investment.