Ugueto, Gustavo A. (Shell Exploration and Production) | Todea, Felix (Shell Canada Limited) | Daredia, Talib (Shell Canada Limited) | Wojtaszek, Magdalena (Shell Global Solutions International) | Huckabee, Paul T. (Shell Exploration and Production) | Reynolds, Alan (Shell Exploration and Production) | Laing, Carson (OptaSense) | Chavarria, J. Andres (OptaSense)
The use of Distributed Acoustic Sensing for Strain Fronts (DAS-SF) is gaining popularity as one of the tools to help characterize the geometries of hydraulic fracs and to assess the far-field efficiencies of stimulation operations in Unconventional Reservoirs. These strain fronts are caused by deformation of the rock during hydraulic fracture stimulation (HFS) which produces a characteristic strain signature measurable by interrogating a glass fiber in wells instrumented with a fiber optic (FO) cable cemented behind casing. This DAS application was first developed by Shell and OptaSense from datasets acquired in the Groundbirch Montney in Canada. In this paper we show examples of DAS-SF in wells stimulated for a variety of completion systems: plug-and-perforating (PnP), open hole packer sleeves (OHPS), as well as, data from a well completed via both ball-activated cemented single point entry sleeves (Ba-cSPES) and coil-tubing activated cemented single point entry sleeves (CTa-cSPES). By measuring the strain fronts during stimulation from nearby offset wells, it was observed that most stimulated stages produced far-field strain gradient responses in the monitor well. When mapped in space, the strain responses were found to agree with and confirm the dominant planar fracture geometry proposed for the Montney, with hydraulic fractures propagating in a direction perpendicular to the minimum stress. However; several unexpected and inconsistent off-azimuth events were also observed during the offset well stimulations in which the strain fronts were detected at locations already stimulated by previous stages. Through further integration and the analysis of multiple data sources, it was discovered that these strain events corresponded with stage isolation defects in the stimulated well, leading to "re-stimulation" of prior fracs and inefficient resource development. The strain front monitoring in the Montney has provided greater confidence in the planar fracture geometry hypothesis for this formation. The high resolution frac geometry information provided by DAS-SF away from the wellbore in the far-field has also enabled us to improve stage offsetting and well azimuth strategies. In addition, identifying the re-stimulation and loss of resource access that occurs with poor stage isolation also shows opportunities for improvement in future completion programs. This in turn, should allow us to optimize operational decisions to more effectively access the intended resource volumes. These datasets show how monitoring high-resolution deformation via FO combined with the integration of other data can provide high confidence insights about stimulation efficiency, frac geometry and well construction defects not available via other means.
Ugueto, Gustavo (Shell Exploration and Production) | Huckabee, Paul (Shell Exploration and Production) | Wojtaszek, Magdalena (Shell Global Solutions International) | Daredia, Talib (Shell Canada Limited) | Reynolds, Alan (Shell Exploration and Production)
It has been widely demonstrated that frac stimulation efficiency and more importantly production, varies significantly between perforation clusters as well as between sleeve entries. Recent trends indicate that many operators are simultaneously increasing the number of perforation clusters or entries while decreasing frac-to-frac spacing. This is done with the expectation that it will lead to more productive wells overall. The purpose of this paper is to investigate some of the aspects that may limit this approach. There are an increasing number of frac diagnostic tools which allow us to get a better understanding of frac placement and production. Unfortunately, there are only few diagnostic tools available today to characterize the near wellbore region (NWR). Fiber Optics (FO) and other downhole measurements can play an important role in providing information about the NWR. In this paper, we share data and examples from wells where the combination of data from Distributed Acoustics Sensing (DAS), Distributed Temperature Sensing (DTS) and downhole gauges is helping us gain insights about this poorly understood region of our unconventional reservoirs. This paper combines DAS, DTS and downhole pressure gauge data to demonstrate the existence of significant near wellbore complexity, both during stimulation and production. We frequently observe changes in DAS signal and pressure during the stimulation of horizontal wells completed via both "Plug and Perf" (PnP) and Cemented Single Point Entry (CSPE) systems. These changes support the existence of significant near-wellbore tortuosity. Furthermore, we show that pressure data from downhole gauges can differ significantly from surface pressure data extrapolated downhole. This can impact the interpretation of Step-Down-Tests, other analytical techniques relying on the surface pressure alone and affecting the calibration of frac models aimed at understanding the NWR. In wells instrumented with a FO cable behind casing, it is possible to use the DTS data during warmback, following stimulation injection to gain insights about frac geometry in the NWR. Such data provides information about the hydraulic frac dimensions created by the stimulation process in both vertical and horizontal wells. During warmback it is easy to distinguish intervals containing hydraulic fractures near the wellbore where the temperature recovery is lagging compared to the unstimulated portions of the well. FO instrumented horizontal wells allow for estimation of the dimensions of the "Frac-Zone" along the wellbore in the NWR where a combination of hydraulically induced longiditunal and vertical transverse fracs exist. Thermal modeling is also presented for selected stages that further support the qualitative interpretation of the DTS. The diagnostics presented help quantify the dimensions of longitudinal and transverse components in horizontal wellbores in the NWR. This paper also highlights the risk of putting perforation clusters or sleeve entries too close to one another. It is clear that the NWR is poorly understood and more information is needed. Understanding the processes that govern the NWR are essential, after all, this is the region where the well and the reservoir interact.
Nikitin, Anton (Shell International Exploration and Production) | Dolan, Sean (Shell International Exploration and Production) | Reiderman, Arcady (Ecotek Inc.) | Grover, Rahul (Schlumberger) | Blount, Aidan (Shell Exploration and Production)
The process by which fluid is lost from a core during retrieval to the surface by hydrocarbon expansion in tight rocks mimics hydrocarbon production under depletion drive in these reservoirs. Therefore, a comparison of hydrocarbon saturation in situ with that of a core sample at standard conditions provides a measure of producible hydrocarbons in tight rocks. From the point of view of hydrocarbon recovery, the core plug can be considered as a reservoir depleted to 1 atm pressure. This of course cannot be achieved physically and hence the difference between the residual hydrocarbon saturation in the plug and that in situ should be regarded as an upper bound on producible hydrocarbon.
The concentration of fluids present in the formation can be directly quantified using NMR T2 measurements. The same measurements can be performed on side wall core samples, at the well site, to quantify the concentration of residual fluid in the core. Thus the two can be compared. Here we will present the results of the analysis of downhole NMR logs and NMR T2 data acquired on side wall samples to identify producible hydrocarbon intervals in a light tight oil formation. The former dataset was acquired using a CMR logging tool by Schlumberger. The latter dataset, NMR measurements on side wall samples, were acquired using an Ecotek SWC-A relaxometer optimized to perform comparable measurements with those of the CMR tool. The comparison of these datasets, at the well site, provides an assessment of in situ producible hydrocarbon in the formation.
The primary objective of this work is to demonstrate how the combination of downhole NMR T2 measurements and NMR T2 measurements on core samples can be used to identify producible hydrocarbons (HC) in Light Tight Oil (LTO) formations. The data used in this study were acquired on an undercharged liquid-rich Organic Rich Shale (ORS) formation, from West Texas, i.e., ORS formations where the volume of HC generated was not sufficient to replace all the water originally deposited in matrix pores.
Ernens, D. (Shell Global Solutions) | Hariharan, H. (Shell International Exploration and Production) | van Haaften, W M. (Shell Global Solutions) | Pasaribu, H. R. (Shell Global Solutions) | Jabs, M. (Shell International Exploration and Production) | McKim, R. (Shell Exploration and Production)
Brazing technology allows metallurgical joining of dissimilar materials using a filler material. In this paper brazing technology applied to casing connections is presented. The initial application was triggered by challenges with mechanical and pressure integrity after expansion of casing connections. Creating a strong bond between the pin and the box could resolve this. Brazing was selected because of the combination of ductility and high bond strength and the relatively fast process to create the bond. The brazing process or temperature-torque-time process (TTT) is performed using regular casing connections, a filler material deposited by flame spray and a flux. Two processes were developed, one for expandable (VM50) grade material and one for quenched and tempered grade material. For this a rig ready (CLASS 1 DIV 1) prototype brazing system was developed consisting of an induction coil as the heat source, an environmental chamber to shield the hot work, and a modified power tong to provide torque. The results of a series of brazing trials on 8-5/8″ and 9-5/8″ casing connections are presented. The brazed connections were subsequently capped end pressure tested, expanded (when applicable) and load cycled. It is concluded that both processes produced leak tight casing connectors before and after expansion (when applicable) as shown by full scale tests
Ugueto C., Gustavo A. (Shell Exploration and Production) | Huckabee, Paul T. (Shell Exploration and Production) | Molenaar, Mathieu M. (Shell Exploration and Production) | Wyker, Brendan (Shell Exploration and Production) | Somanchi, Kiran (Shell Exploration and Production)
It is now well established that the production from horizontal wells completed via hydraulic fracture stimulations (fracs) is highly variable along the length of the wellbore. In addition to subsurface conditions, elements of the completion design, such as fluid volume, proppant tonnage, rate, stage length, the number of perforation clusters and their spacing, influence the performance of individual stimulated intervals and wells. Information about completion efficiency can be obtained using Fiber Optic (FO) diagnostics. Distributed Temperature Sensing (DTS) and Distributed Acoustic Sensing (DAS) provide great insights into the factors controlling frac construction and performance of each perforation cluster. The integrated analysis of DAS and DTS in horizontal wells completed with multiple perforation clusters per stage indicate that, although most perforation clusters receive fluids during the stimulation, there are significant changes in efficiency during the frac stimulation process that can impact frac connectivity, conductivity and ultimately, their production. This presentation illustrates recent observations about Perforation Cluster Efficiency (PCE) using FO diagnostics and summarizes the results for many wells with Cemented Plug and Perforated completions Limited Entry design (CPnP LE).
Corradetti, A. (DiSTAR - Università di Napoli Federico II) | Girundo, M. (DiSTAR - Università di Napoli Federico II) | Tavani, S. (DiSTAR - Università di Napoli Federico II) | Iannace, A. (DiSTAR - Università di Napoli Federico II) | Parente, M. (DiSTAR - Università di Napoli Federico II) | Mazzoli, S. (DiSTAR - Università di Napoli Federico II) | Strauss, C. (Shell Exploration and Production) | Torrieri, S. (Shell Exploration and Production) | Pirmez, C. (Shell Exploration and Production) | Giorgioni, M. (Shell Exploration and Production)
Hauterivian-Barremian dolomitized carbonates of the Monte Faito ridge (Sorrento peninsula, Italy) rep-resent a good analogue for the Lower to middle Cretaceous portion of the reservoir units of the Southern Italy oilfields. In order to gain a better understanding of the distribution of reservoir-scale, flow-controlling ‘fracture corridors’ and of the nature of the mechanical boundaries con-trolling their vertical propagation, an integrated sedimentological, petrographic and structural study has been performed on a 200 m-thick succession of alternating dolostones and limestones. The fracture analysis, performed on a 3D model generated from photogrammetry with the help of an Unmanned Aer-ial Vehicle, identified a clear mechanical stratigraphy for large-scale fracture corridors and fault damage zones. The following stratigraphic survey established that the position of the main mechanical interfaces is controlled by: (i) tens of meters-thick bed packages dominated by fine- to medium-grained dolomite abutting a package of thick calcareous or calcareous-dolomitic beds; and (ii) packages of thin laminated dolomitic beds, representing thinning upward cycles deposited during the late highstand of lower order cycles. The rather regular stacking pattern resulting from the superposition of several orders of shallow-ing-upward cyclicity may be used to obtain a predictive tool for fracture distribution and impedance.
Hard substrates associated with offshore oil and gas platforms can contribute to the productivity of marine ecosystems, thereby generating local and regional economic benefits. These benefits form the basis for incorporating the platform into a rigs-to-reefs program when it is retired or for selecting some other type of removal option. There are many options for reefing platforms, each differing in environmental impact associated with dismantling and transport of the platform structure (deck, jacket, and other subsea structures). The use of science-based decision making in exploring platform-removal options can be beneficial for all stakeholders in the context of regulatory environment, complex ecosystem, and human interactions across multiple scales. Accommodating these complexities in a decisionmaking process is the foundation of an ecosystem-based-management (EBM) approach. EBM is an environmental-management approach that recognizes the full array of interactions within an ecosystem, including humans, rather than considering single issues, species, or ecosystem services in isolation (Christensen et al. 1996; McLeod et al. 2005; Altman et al. 2011).
The focus of this study is on one of Shell's former deepwater assets in the Gulf of Mexico. The fixed-jacket platform has been in operation for more than 35 years and extends to more than 1,000 ft of water depth off the coast of Louisiana. Few studies have been published on the ecology of marine life inhabiting deepwater platforms such as these. To begin to understand the specific contribution of this platform as an artificial reef, a stratified (across depth down the platform) study was performed by use of routinely collected remotely-operated-vessel (ROV) video footage to assess fish and sessile biotic communities. The ROV study revealed clear depth-related patterns of visually conspicuous epibiota (surface-dwelling organisms such as Lophelia pertusa) and numerous species of reef and pelagic fishes. These data were used to construct a matrix to rank the ecosystem services of several decommissioning alternatives, including complete removal of the deck and jacket; removal of the deck, topping the jacket 85 ft below the waterline, and leaving the remainder in place; and removal of the deck and transfer of the entire jacket to a rigs-to-reef location. This portion of the assessment provided a strategic framework for identifying and evaluating sensitive ecosystem services in association with both human and environmental drivers to provide realistic (actionable) guidance in the selection of these decommissioning options. The preliminary ranking illustrated that a high level of ecosystem services could be maintained by decommissioning alternatives that leave the jacket in place or transfer the jacket elsewhere as part of a rigs-to-reefs program.
Well cementing is a crucial component of deepwater well construction, and a key to cementing success is the performance of the cementing plug. Plug performance is primarily based on the mechanical wiping efficiency and wear resistance of the plug. However, limited understanding of the performance has hindered the establishment of standards. While API RP10F provides recommended testing practices to evaluate the performance of cementing float equipment, it does not include cementing plugs.
This paper is the first published review of efforts to better understand cement plug performance and to establish industry standards. Through laboratory studies, it examines material loss in actual deepwater applications and evaluates the effect on wiping performance of cementing plugs. These studies provide the basis of a selection process for wear-resistant materials. The paper also examines methods of measuring wiping efficiency and overall plug performance. Based on these methods, a proposal is presented for establishing industry performance standards for setting cementing plugs.
Cementing wiper plugs provide a physical barrier to cement contamination by separating displacement fluid and wiping residual mud film and other materials from the inside surface of the pipe. Separation and wiping efficiency are directly related to plug wear resistance and to the process of balancing design to achieve optimal stiffness and pressure containment. This design balance is achieved through rigorous material testing and design refinement. Analysis of wiper cuttings samples has provided a clear understanding of the plug's ability to provide a physical barrier to separate fluids and how that affects the function of downhole tools. This cuttings evaluation has provided information on material loss and positive fin interference. Results of the evaluation are corroborated by field performance achieved in cementing lengths of casing greater than 16,000 ft.
Plug wear is of particular concern in long, high-volume, deepwater casing strings where it can lead to displacement errors and reliability problems for downhole pressure-actuated tools. These displacement errors are examined in field applications that precisely locate the plug at multiple points during the cementing process.
Hard substrate associated with offshore oil and gas platforms can contribute to the productivity of marine ecosystems thereby generating local and regional economic benefits. These benefits form the basis for incorporating the platform into a rigs-to-reefs program when it is retired or selecting some other type of removal option. There are many options for reefing platforms, each differing in environment impact of activities associated with the dismantling and transport of the platform structure (deck, jacket, and other subsea structures). Utilizing science-based decision making in exploring platform removal options can be beneficial for all stakeholders in the context of a regulatory environment, complex ecosystem, and human interactions across multiple scales. Accomodating these complexities in a decision making process is the foundation of an Ecosystem Based Management (EBM) approach. EBM is an environmental management approach that recognizes the full array of interactions within an ecosystem, including humans, rather than considering single issues, species, or ecosystem services in isolation (
The focus of this study is on one of Shell's deepwater assets in the Gulf of Mexico. The fixed jacket platform has been in operation for more than 35 years and extends to over 1,000 feet of water depth of the coast of Louisiana. Few studies have been published on the ecology of marine life inhabiting deepwater platforms such as these. To begin to understand the specific contribution of this platform as an artificial reef, a stratified (across depth down the platform) study was performed using routinely collected Remotely Operated Vessel (ROV) video footage to assess fish and sessile biotic communities. The results of the ROV study revealed clear depth-related patterns for visually conspicuous epibiota (
The objective of this research was to investigate the potential effect of expandable-casing technology on the cement sheath and remediation of sustained casing pressure (SCP) caused by microannular gas migration. Varying magnitudes of SCP exist in the Gulf of Mexico, where more than 80% of casing strings exhibiting SCP are production and surface casings, representing a great technical, economic, and environmental risk. Situations in which SCP is observed usually result in costly and frequently unsuccessful remediation efforts. A unique bench-scale physical model was used to simulate expansion of a previously cemented casing under field-like conditions. Experimental measurements obtained before and after low percentage pipe expansion exhibited improvement of cement/pipe interface. Successful multirate flow-through experiments with nitrogen gas showed the effectiveness of this technique in sealing of microannular-gas-leakage pathways, providing ideal remediation of SCP immediately post-expansion; and after up to 60 days of post-expansion, the seal integrity was intact.