A review of basic well log interpretation techniques in highly deviated wells

Abstract

Drilling deviated wells has become customary in recent times. This work condenses various highly deviated and horizontal well log interpretation techniques supported by field examples. Compared to that in vertical wells, log interpretation in highly deviated wells is complex because the readings are affected not only by the host bed but also the adjacent beds and additional wellbore-related issues. However, understanding the potential pitfalls and combining information from multiple logs can address some of the challenges. For example, a non-azimuthally focused gamma ray logging while drilling (LWD) tool, used in combination with azimuthally focused density and neutron porosity tools, can accurately tell if an adjacent approaching bed is overlying or underlying. Moreover, resistivity logs in horizontal wells are effective in detecting the presence of adjacent beds. Although the horns associated with resistivity measurements in highly deviated wells are unwanted, their sizes can provide important clues about the angle of the borehole with respect to the intersecting beds. Inversion of horizontal/deviated well logs can also help determine true formation resistivities. Additionally, observed disagreement between resistivity readings with nuclear magnetic resonance (NMR) T2 hydrocarbon peaks can indicate the presence or absence of hydrocarbons. Furthermore, variations in pulsed neutron capture cross sections along horizontal wells, measured while injecting various fluids, can indicate high porosity/permeability unperforated productive zones. Finally, great advances have been made in the direction of the bed geometry determination and geologic modeling using the mentioned deviated well logs. More attention is required toward quantitative log interpretation in horizontal/high angle wells for determining the amount of hydrocarbons in place.

Estimating Total Organic Carbon (TOC) Content and Porosity of the Ranikot Formation in the Central Indus Basin, Pakistan, Using Seismic Inversion and Well Log Analysis

“…Predicting the distribution of porosity in sandstone reservoirs can be challenging due to variations in depositional conditions, the presence of heterogeneous lithofacies, and the repetition of pore size variations [41,42]. Gamma-ray, density, resistivity, and neutron logs are commonly used for formation evaluation [43]. The well-log data of the Mehar-02 well was analyzed to determine the subdivisions of the Ranikot Formation.…”

Establishment and Application of a Pattern for Identifying Sedimentary Microfacies of a Single Horizontal Well: An Example from the Eastern Transition Block in the Daqing Oilfield, Songliao Basin, China

“…The first horizontal well was constructed in Daqing Oilfield in 1991, and its output was 4-8 times that of the surrounding vertical wells. With the continuous improvement in logging technology and instruments, rapid progress has been made in recent years in horizontal-well-related technologies and construction [1][2][3], for instance, in horizontal well logging interpretation [4][5][6][7], drilling technology [8][9][10], completion technology [11][12][13], fracturing technology [14,15], development program optimization [16,17], and geologic steering [18,19]. Although many scholars have studied sedimentary microfacies, most have focused on vertical wells, and relatively few have studied sedimentary microfacies by combining horizontal and vertical wells to establish the pattern for identifying sedimentary microfacies of single horizontal wells.…”