A Novel Workflow for Well Placement Optimization Within Highly Fractured Carbonate Reservoirs Through the Integration of Rock and Reservoir Fluid Geochemistry Measurements and Petrophysical Log Data: A Multiwell Field Case Study, Adiyaman, Turkey
Authors:   Geolog International, Hekimoglu Kemal C. , Turkmen Melike O. ,   Turkish Petroleum Corporation (TPAO), Yuruker Onur ,   Turkish Petroleum Corporation (TPAO), Yildirim Elif Cihan ,   Turkish Petroleum Corporation (TPAO), Biterge Mustafa ,   Turkish Petroleum Corporation (TPAO)
Published: November 2024

The structural complexities in the southeast of Turkey create considerable challenges, as production is limited to the accumulations within confined zones dictated by fracture systems and flow dynamics, where favorable rock, reservoir, and fluid properties coexist. The diagenetic processes in these carbonates result in rapid variation in the rock matrix and complex pore distribution. Therefore, the assessment of petrophysical properties necessary for the efficient exploitation of hydrocarbon-bearing carbonates is crucial. A series of lateral wells were drilled in a recent production campaign within these fields with the aim of optimizing production. Homogeneous gamma/resistivity responses from these clean carbonate reservoir rocks and the borehole tortuosity issues related to hole instability created limitations with the traditional approach of using LWD data for geosteering. Also, the lack of local experience in drilling laterals in the area, far behind bit measurements, created additional challenges for geosteering using conventional methods, therefore necessitating a novel approach. The objectives of this paper include (a) integrating petrophysical log data with surface mineralogy for rock classification, (b) establishing expected responses from surface data in relation to the modeled rock classifications, (c) generating a vendor-independent geosteering workflow to standardize the real-time surface/downhole data QC procedures and the rules for steering decisions. Conventional techniques were employed to capture variations in the rock properties using available petrophysical log data (spectral GR, resistivity, density, porosity, SP, DT, image, neutron spectroscopy) from 20 offset wells. The 1,508 drill-cutting samples from the same offset wells were analyzed in-lab to measure the inorganic geochemical compositions. Data resolution was synthetically increased using conventional interpolation methods through the qualitative correlation with spectroscopy log data where limited legacy cuttings data from offset wells were available within targeted zones. Estimation of the rock properties to establish analogs to be followed during drilling required the integration of rock mineralogy and petrophysical data. A dedicated prewell model was constructed for each of the 10 lateral wells within the campaign using log data, rock geochemistry measurements, and seismic interpretations. During the drilling of the laterals, detailed geochemical characterization using ED-XRF and XRD analysis from cuttings sampled at high frequency (every 1 to 2 m), quantitative mud gas measurements (C1 to C5), and LWD logs (azimuthal GR and resistivity) were integrated in real time. These data were used to visualize and interpret the relative stratigraphic position, the relative hydrocarbon saturation, and fracture/fault distribution along the wellbore. The geochemical compositions of the cavings recovered were analyzed to allocate their origination depth using a hierarchical clustering approach. Finally, a dedicated workflow was created to streamline the decision-making process for steering between the operator’s production and engineering department, the directional drilling subcontractors, the geosteering, and the geochemistry specialist. The proposed workflow was refined with experiences during the course of the campaign and was applied to the 10 lateral wells collaborating with multiple directional drilling and geosteering service providers. Employing all geosteering techniques (model/stratigraphy based, multiwell, and multilog), it was possible to land, navigate, and reach well TD keeping an average of > 90% inside the target, giving the operator’s reservoir team better information to make decisions in real time. We demonstrated that when sedimentary diagenetic factors are favorable, it is possible to detect fracture and fault systems through the measurements of a variety of mineral species precipitated. Furthermore, the structural displacement degree was possible to be evaluated through the correlation of the geochemical fingerprint of the rocks before and after faults. Breakout zones within the wellbore were identified through the geochemistry-based statistical cavings allocation methodology described and later were correlated and confirmed with image logs. This assessment was used to support the drilling decisions and procedures to be utilized. A unique contribution of the proposed workflow is to establish a detailed methodology to integrate a diverse data set of rock and reservoir fluid geochemistry and petrophysical measurements to optimize rock classification and support formation evaluation efforts. The workflow aims to improve the procedures compared to similar applications in the past in terms of the variety of measurement techniques used and the vendor-independent nature of the implementation. This approach is crucial to establishing a communication standard between multiple service providers and departments within the operator organization with the sole objective of streamlining the geosteering decisions.