Total Systems Approach to Reduce Fouling and Improve System Efficiency Using Hydrogen Sulfide Scavengers

The Cotton Valley sand and Haynesville shale formations are situated in East Texas, USA, producing oil, gas, and condensate on land. Most of the producing assets are mature and souring, and the presence of hydrogen sulfide in the produced fluids and gas provides both operational concerns in terms of solids deposition and asset integrity in the production facilities as well as complexity when considering the processing, export, and sale of condensate and gas. Produced gas was traditionally treated with MEA triazine hydrogen sulfide scavenger prior to liquification by LNG plant. There have been historical issues with both the levels of hydrogen sulfide left in the gas and also solids formation in the process, which threatened periodic shutdown of the LNG plant. A holistic approach was used to improve the overall sulfur removal process. This includes the reduction or elimination of solids formation as well as improvement in the system scavenging efficiency. The approach considered current operating procedures, system parameters, equipment design (contactors), and H2S scavenger chemistry.

Dynamic modeling of bedding-plane slip during hydraulic fracturing

Whether the tip stresses around a dynamically propagating hydraulic fracture (HF) could activate a bedding plane (BP) or not is an important question for HF propagation and microseismicity generation. BP slip has been proposed to be one main source of microseismicity during HF treatments in unconventional reservoirs. However, a BP perpendicular to a principal stress direction is unlikely to be activated in a simple geomechanical model. We have applied a dynamic finite-element geomechanics method to examine the induced dynamic shear stress and the activation of BPs that are perpendicular to the HF based on the Cotton-Valley tight-sand reservoir properties. We work in a 2D vertical-plane framework. The induced dynamic stresses around a HF tip could be significant. We explore three different scenarios for the BP activation. In the first scenario, an HF is dynamically propagating toward two symmetric BPs, but has not touched them yet. We find that only low-strength BPs can be activated in this scenario. In the second scenario, an HF dynamically propagates toward two symmetric BPs and then it crosses them by a short distance. The BPs could be more easily activated in this scenario compared with the first scenario. The slip length and maximum slip decrease with cohesion, critical slip distance, or maximum principal stress. In the third scenario, an HF dynamically propagates toward two symmetric BPs, and then fluid invasion into the BPs occurs after the HF touches them. Large shear slippage and slip length happen in this scenario because fluid invasion weakens the BPs. In all of the scenarios, different senses of shear could occur along the BPs and a rupture typically propagates bilaterally from the initiation point on the BPs.

Upper Jurassic Tithonian-centered source mapping in the deepwater northern Gulf of Mexico

Long the subject of speculation, the origin, distribution, and quality of Mesozoic source beds in the deepwater Gulf of Mexico (GOM) are now open to analytical study and hypothesis. We have developed new maps and concepts for organic richness and lithofacies patterns of the primary Upper Jurassic oil-prone source rock interval spanning the Kimmeridgian to Lower Berriasian in the northern GOM. This interval, previously referred to as the Tithonian-centered source, includes the Haynesville and Bossier shales, which lie within supersequences representing second-order transgressive and high-stand systems tracts, respectively. A newly developed gulf-wide Cotton Valley-Bossier paleogeographic map based on a novel paleotectonic model for the Mesozoic provides the framework for this source mapping study. Organic richness averages up to 4.7% and 6.5% total organic carbon for the Kimmeridgian and Tithonian-Lower Berriasian supersequences, respectively, based on the log overlay [Formula: see text] technique and increases toward the basin center. Lithofacies-sensitive geochemical parameters from reservoired oils and oil seeps tied to the Tithonian-centered oil family demonstrate several potential entry locations for siliciclastic sediments into the Tithonian distal calcareous environment. The region from Garden Banks to Alaminos Canyon appears to be the locus of siliciclastic mixing with carbonates in the deepwater and link with updip evidence of a wide progradational clastic apron sourced by the paleo-Mississippi river. This siliciclastic input may contribute to the potential for improved oil quality by lowering the content of sulfur incorporated into kerogen moving southwest from Ewing Bank-Mississippi Canyon to Alaminos Canyon. Ultimately, enhanced Upper Jurassic source deposition ended with a ventilation event whereby more oxygenated, deeper water entered the northern GOM. Declines in calculated total organic carbon occurring later to the west during the earliest Cretaceous (Berriasian) indicate the opening of the gateway between the GOM and the central Atlantic possibly related to the termination of seafloor spreading in the eastern GOM.

Challenges to Geosteering and Completion Optimization of Horizontal Wells in the Cotton Valley Formation, East Texas

Summary Cotton Valley tight gas sands in the East Texas basin of North America consist of very-fine-grained, well-sorted quartz arenites and subarkoses that are overprinted by significant diagenetic processes. Stratigraphic variations in rock type control gas production. Hydraulic fracturing delivers economic gas production. We drilled horizontal wells more than 4,000 ft long consisting of more than 12 hydraulic-fracturing stages. The good gas-producing rock-type reservoirs are usually less than 14-ft thick and exhibit strong diagenetic overprint. Low gas prices challenge the use of sophisticated geosteering logs. By use of a very-basic gamma ray (GR) log and very-limited offset-pilot-well data, chasing such thin and variable sand bodies over a distance of 4,000 ft in a marginal marine sedimentary environment is daunting. Apart from this, horizontal wells that target thin layers present unique challenges to completion optimization. We acquired quad-combo log data, including azimuthal-density image data, by use of a logging-while-drilling (LWD) tool. We performed extensive log modeling by combining the horizontal well logs with logs from the two offset vertical wells, and achieved consistent interpretation. Log modeling has helped the post-drill well diagnosis in geosteering, completion design, and production performance. It has also supported formation evaluation. This study will highlight an integrated-study work flow in tight gas sands by use of openhole and cased-hole data. It will demonstrate the geosteering challenges, explain the log-modeling process, and display the formation-evaluation results. Geomechanical study, together with hydraulic-fracturing data and production-log data, will be used to confirm that good gas-producing rock types are easier to fracture, and they contribute better to production.