The presentation “INTEGRATED APPLICATION OF ADVANCED LOGGING-WHILE-DRILLING FOR UNDERSTANDING ALTERED BASEMENT ROCKS: A CASE STUDY FROM THE NORWEGIAN NORTH SEA” will be given by Sayyid Ahmad, from Halliburton.
Abstract
Altered basement rocks have been identified as part of petroleum reservoirs in some Norwegian North Sea oilfields. The challenges when targeting altered basement rocks during drilling are the high degree of variation over short distances, uncertainty related to productivity, and reservoir quality. Extensive outcrop and well studies, integrated with core and other available log data, show that these basement facies can be subdivided into specific categories controlled by fractures and the degree of physio-chemical alteration. Recently, an infill campaign was executed in Field A, where a horizontal well targeted these altered basement rocks, in addition to some conglomerates. The objective of this case study is to present an integrated workflow using real-time advanced logging-while-drilling (LWD) data and surface measurement interpretations to understand the basement facies architecture. This approach has the potential to facilitate wellbore placement decisions and optimize completion design within these physio-chemically altered intervals.
By using advanced LWD data set and integrated interpretation workflow, it was possible to map conglomerates and basement intervals using ultra-deep azimuthal resistivity (UDAR) and conventional log data. X-ray Fluorescence (XRF) elemental cross-plots (Total Alkali Silica (TAS) diagram for igneous rocks based on the relationship between SiO2 vs Na2O+K2O) were also integrated to identify basement intervals with various chemical compositions. As a result, three main basement units were observed: Unit 1, with very high resistivity, interpreted as dioritic basement from TAS diagram and conventional log measurements; Unit 2, with medium resistivity and lateral sharp changes in resistivity, interpreted as granodioritic by using TAS diagram and conventional log measurements;; and Unit 3, with medium to high UDAR resistivity, and with lateral sharp changes in resistivity, interpreted as granitic by using TAS diagram and conventional log measurements. By integrating detailed ultrasonic image interpretation and Nuclear magnetic resonance (NMR) data, the basement was further subdivided into different specific image facies types. Dioritic basement was described with four different image textures, fractures of differing type, intensity and qualitative width, and multimodal NMR T1 distributions. Only within this interval, cemented low and high-angle higher acoustic impedance mineral-filled veins were interpreted. During formation pressure testing low mobility was observed within this zone. Granitic basement was also dominated by three different image textures. As a result, a comprehensive approach of data gathering and integrated interpretation in real time helped to design suitable completions and placement of packers and screens with good confidence.
Biography
Sayyid Ahmad is a geoscientist and image log analyst with the Geoscience & Production group at Halliburton in Norway. At Halliburton, his areas of interest include integrated interpretation of advanced log data. Sayyid has previously worked in Norway, Pakistan, and Houston USA as an explorationist where his areas of interest were seismic interpretation, AVO, seismic inversion, synthetic seismic modeling (convolutional and viscoelastic) and seismic processing. He holds a PhD degree in geophysics from the University of Stavanger, Norway, an MS degree in petroleum geoscience engineering from the University of Stavanger, Norway, and bachelor’s in mathematics and physics from Quaid-I-Azam University of Pakistan.