Application of Production Geochemistry in Unconventional Reservoirs (Production Allocation and Beyond)
While reservoir geochemistry in field development of conventional reservoirs for predicting fluid properties and understanding compartmentalization has been established for several decades, application of production geochemistry in tight unconventional reservoirs (source rocks and hybrid systems) is only now becoming widely recognized and applied. There are a plethora of challenges and uncertainties in these ultra-low permeability formations that can be addressed with the use of production geochemistry, which is cost effective and delivers a high value of information. One of most important applications necessary for determining optimal lateral stacking and spacing development strategies is characterizing the extent and behavior of vertical drainage surrounding horizontal fracture-stimulated wells. There has been a concerted industry effort to understand the dimensions and efficacy of the stimulated rock volume (SRV) using diagnostic technologies such as monitoring microseismic events, chemical tracers, fiber optics, pressure gauges, interference testing and horizontal cores. However, there are few inexpensive and robust methods designed to monitor vertical or cross well drainage, referred to here as the drained rock volume (DRV). To overcome this challenge, ConocoPhillips developed a novel geochemical-based methodology using production allocation of produced hydrocarbons collected in time-series and calibrated to core extracted oils to cost effectively ascertain vertical drainage of unconventional wells (Jweda et al., 2017; Liu et al., 2017). Time-lapse geochemistry (TLG) monitoring provides insight into several aspects of production in unconventional reservoirs. TLG can be used to ascertain vertical drainage heights and vertical connectivity between stacked wells, evaluate the efficacy of different completion designs, identify the source of external gas production, and understand the physics of enhanced oil recovery efforts. Time-series aqueous geochemistry of produced water is another technology that provides additional information about drainage dynamics in unconventional reservoirs. A deeper understanding of the provenance(s) and change(s) in composition with time of these returned waters, which involve water-rock reactions and fluid exchanges between hydraulic and formation fluids, is also critical information for field management and optimization. Here we present an overview of the TLG technique and its applications to a variety of development challenges (e.g. shale vs. hybrid plays) in examples from assorted North America ConocoPhillips unconventional plays. We show that the ‘fingerprints’ of the produced fluids can be quantitatively linked using core data to specific stratigraphic layers within these formations. Key insights from these analyses are that vertical drainage is limited and dynamic during production, sometimes shrinking with time depending on the completion design. Results from these TLG projects have been integrated with multiple well pilot datasets (e.g. microseismic, soluble tracers, cores, image logs, pressure gauges in vertical and horizontal wells, and permanently installed fiber optic cables) to optimize ConocoPhillips’ development strategies.
AAPG Datapages/Search and Discovery Article #90349 © 2019 AAPG Hedberg Conference, The Evolution of Petroleum Systems Analysis: Changing of the Guard from Late Mature Experts to Peak Generating Staff, Houston, Texas, March 4-6, 2019