A New Mineralogy Cuttings Analysis Workflow for Optimized Horizontal Fracture-Stage Placement in Organic Shale Reservoirs

Abstract

The dominant methods of geosteering and horizontal formation evaluation in most organic source rock reservoirs has been limited to the use of logging-while-drilling (LWD) gamma ray and conventional mud logging. This limitation is primarily attributable to cost constraints and the historical preference for geometric fracture-stage placement. This process has resulted in varied performance between closely spaced wells thought to be drilled in similar stratigraphic positions and like rock. Very little new vertical well data is typically acquired in the development phases of most of these plays to document any changing physical rock properties that may contribute to the variable performance between wells. The perceived cost of additional pilot wells or additional horizontal LWD, open hole, or cased-hole measurements restricts most operational teams to a situation in which best practices may be recognized but are rarely implemented. To address this issue, this paper proposes and presents a cost effective cuttings analysis workflow, using a new combination of available technologies that is calibrated to vertical and horizontal petrophysical and mechanical properties. An automated fracture-stage and cluster placement method using this analysis workflow is applied to validate well treatment and post-fracture performance. In recent years, several tools have been developed to analyze drill cuttings from oil and gas wells. The most commonly used tools include X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM) combined with energy dispersive X-ray spectroscopy (EDX), bulk density, and pyrolysis. Although each of these tools can be used to develop a limited determination of the in-situ rock character, the combination of three of these tools (XRF, SEM/EDX, and pyrolysis) can provide a more comprehensive picture of formation properties. The combination of XRF analysis with the SEM/EDX analysis is the key to the cuttings workflow. The exact location within the borehole can be determined and a robust mineralogy developed that is independent of normative mineralogy (typical XRF) or operator-interpretive mineralogy (XRD). Additional outputs include relative brittleness index, bulk density, lithology, fractional and textural relationships, total organic carbon (TOC) proxy, and a new porosity index. Trace and major elemental ratios are also available for precise stratigraphic placement. The addition of cuttings pyrolysis enables hydrocarbon typing, producible hydrocarbons, TOC, and total inorganic carbon (TIC) within each sample to be established. In this paper, outputs from the XRF-SEM/EDX-pyrolysis analysis of two vertically cored wells are benchmarked against complete vertical log suites for the modeling of petrophysical and mechanical properties. Subsequent horizontal cuttings properties for the two area examples, Marcellus and Eagle Ford Shales respectively, are presented and analyzed with the vertical modeling applied. In addition, the Eagle Ford horizontal cuttings analysis results are compared and contrasted with a through-casing pulsed neutron log (PNL) for potential upscaling of the sample frequency for continuous physical properties evaluation, including effective porosity. The exact stratigraphic placement from only a cuttings analysis is also demonstrated. Finally, the calibrated Eagle Ford and Marcellus horizontal cuttings analyses are used as inputs for an optimized fracture-stage and perforation cluster placement design for each of the wells. For validation, individual fracture-stage pumping performance is compared to the predicted formation properties from the Eagle Ford cuttings analysis example.

Selecting optimum log measurements for hydraulic fracturing

“…This work focuses primarily on the production index (PI), fracture index (FI; Buller et al, 2014), and TOC as the key parameters for hydraulic fracturing. PI contains other petrophysical properties (equation 1) that are related to rock fabric.…”

“…It can be measured from horizontal openhole neutron-density logs, pulsed neu- SF126 Interpretation / May 2016 tron cased hole porosity with inelastic density, or cuttings-based scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX) porosity with a pyrolysis-based kerogen porosity proxy (e.g., Buller et al, 2014). It can be measured from horizontal openhole neutron-density logs, pulsed neu- SF126 Interpretation / May 2016 tron cased hole porosity with inelastic density, or cuttings-based scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX) porosity with a pyrolysis-based kerogen porosity proxy (e.g., Buller et al, 2014).…”

“…For the development of oil and gas fields, it is important to know the optimal logging suites for selecting perforation stages (e.g., Buller et al, 2014) for future wells. Horizontal fracture staging is generally not an optimized process and results in wasted completion expenses (e.g., Buller et al, 2010aBuller et al, , 2010b.…”

Restimulation Design Considerations and Case Studies of Haynesville Shale

“…The methodology to perform this relies on obtaining the best petrophysical model available for the field and projecting the data across the wellbore through a geosteering interpretation of the logging-whiledrilling data acquired during the drilling of the well. Additional data can be used if available, such as cuttings analysis or any available open hole or cased hole logs of the lateral (Buller et al 2014). …”

Mineralogical assemblage of Cambay Shale of North Cambay Basin, Gujarat, India

“…Linear Swelling Meter, Cation Exchange Capacity (Abouelresh et al 2016) and Quantitative Evaluation of Minerals Using Scanning Electron Microscopy (QEMSCAN), QEMSCAN coupled with CT Scanning (Ahmad and Haghighi 2012), Pulse Neutron Spectrometry Tool (Jacobson et al 2009) have also been used to assess the distribution of different minerals in a porous samples. Therefore, FTIR, XRD and SEM are the most commonly and frequently used characterization technique for mineralogical assessment (Buller et al 2014, Abouelresh et al 2016, Rodriguez et al 2015, Guerra et al 2017, Akbar et al (2017, Yang et al 2018). However, for the identification of elemental composition of shales, X-ray fluorescence or energy dispersive XRF is the most commonly used technique (Guerra et al 2017;Turner et al 2015;Abouelresh et al 2016;Rodriguez et al 2015).…”