Surface Processing Efficiency Research Articles

Systematic Coiled-Tubing-Efficiency Improvement Reduces Operational Time

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 184779, “Consistent, Systematic Approach to Deepwater Coiled-Tubing-Efficiency Improvement Substantially Reduces Operational Time, Gulf of Mexico,” by Peter Weiland, SPE, Alexander Rudnik, SPE, and Eric Gagen, SPE, Schlumberger, prepared for the 2017 SPE/ICoTA Coiled Tubing and Well Intervention Conference and Exhibition, Houston, 21–22 March. The paper has not been peer reviewed. Deepwater coiled-tubing (CT) well interventions can benefit from significant rig-time reduction and cost savings associated with improved efficiencies of surface processes. Efficiency improvement requires a systematic approach and detailed analysis of each part of the process. The efficiency methodology allows for systematic improvement in all areas of CT operations, specifically for surface activities. The total efficiency solution described in this paper requires no additional cost to service providers, and results can be seen immediately. Deepwater Coiled Tubing The use of CT for well intervention can provide many downhole solutions throughout the life of a well. Although there is much discussion of the financial and technical aspects of CT in the industry, less conversation is directed toward the efficiency of CT surface processes. The expansion of analysis, specifically to CT process efficiency both before and after in-hole operations, is necessary for a holistic approach to total efficiency improvement. The stages of CT operation shown in green in Fig. 1 can be identified as five distinct surface activities. Design Methodology The first stage of the efficiency solution involved analysis of past performance. Some limited performance data were collected and reviewed, primarily on CT rig up, pressure testing, and transition time between CT and wire services (wireline and slickline). The underlying strategies of several widely accepted continuous-improvement programs, such as lean principles and the define/measure/analyze/implement/control methodology, were used to provide the link between performance and improvement. Low-performance areas and areas of recurring nonproductive time (NPT) were addressed through root-cause analysis and remedial-work plans that were focused on specific tasks. Mean-while, high-performance areas were analyzed to document the best practices for efficient operational execution so that efficiency gains could be realized for the duration of the campaign. Performance is compared with both baseline and previous-operation performance data so that trends and inconsistencies could be identified easily. Equipment Mobilization/Demobilization and Lifting The first stage of any CT operation involves mobilizing the required equipment to location. A typical CT spread may require 30 to 45 individual lifts to move equipment from the workboat to the rig. This first process, termed boat work and equipment spotting, is most commonly tracked by total time required to place the entire CT spread on deck.

Spatiotemporal trends in erosion rates across a pronounced rainfall gradient: Examples from the southern Central Andes

The tectonic and climatic boundary conditions of the broken foreland and the orogen interior of the southern Central Andes of northwestern Argentina cause strong contrasts in elevation, rainfall, and surface-process regimes. The climatic gradient in this region ranges from the wet, windward eastern flanks (~2m/yr rainfall) to progressively drier western basins and ranges (~0.1m/yr) bordering the arid Altiplano–Puna Plateau. In this study, we analyze the impact of spatiotemporal climatic gradients on surface erosion: First, we present 41 new catchment-mean erosion rates derived from cosmogenic nuclide inventories to document spatial erosion patterns. Second, we re-evaluate paleoclimatic records from the Calchaquíes basin (66°W, 26°S), a large intermontane basin bordered by high (>4.5km) mountain ranges, to demonstrate temporal variations in erosion rates associated with changing climatic boundary conditions during the late Pleistocene and Holocene. Three key observations in this region emphasize the importance of climatic parameters on the efficiency of surface processes in space and time: (1) First-order spatial patterns of erosion rates can be explained by a simple specific stream power (SSP) approach. We explicitly account for discharge by routing high-resolution, satellite derived rainfall. This is important as the steep climatic gradient results in a highly nonlinear relation between drainage area and discharge. This relation indicates that erosion rates (ER) scale with ER~SSP1.4 on cosmogenic-nuclide time scales. (2) We identify an intrinsic channel-slope behavior in different climatic compartments. Channel slopes in dry areas (<0.25m/yr rainfall) are slightly steeper than in wet areas (>0.75m/yr) with equal drainage areas, thus compensating lower amounts of discharge with steeper slopes. (3) Erosion rates can vary by an order of magnitude between presently dry (~0.05mm/yr) and well-defined late Pleistocene humid (~0.5mm/yr) conditions within an intermontane basin. Overall, we document a strong climatic impact on erosion rates and channel slopes. We suggest that rainfall reaching areas with steeper channel slopes in the orogen interior during wetter climate periods results in intensified sediment mass transport, which is primarily responsible for maintaining the balance between surface uplift, erosion, sediment routing and transient storage in the orogen.

Quantifying bedrock-fracture patterns within the shallow subsurface: Implications for rock mass strength, bedrock landslides, and erodibility

[1] The role of bedrock fractures and rock mass strength is often considered a primary influence on the efficiency of surface processes and the morphology of landscapes. Quantifying bedrock characteristics at hillslope scales, however, has proven difficult. Here, we present a new field-based method for quantifying the depth and apparent density of bedrock fractures within the shallow subsurface based on seismic refraction surveys. We examine variations in subsurface fracture patterns in both Fiordland and the Southern Alps of New Zealand to better constrain the influence of bedrock properties in governing rates and patterns of landslides, as well as the morphology of threshold landscapes. We argue that intense tectonic deformation produces uniform bedrock fracturing with depth, whereas geomorphic processes produce strong fracture gradients focused within the shallow subsurface. Additionally, we argue that hillslope strength and stability are functions of both the intact rock strength and the density of bedrock fractures, such that for a given intact rock strength, a threshold fracture-density exists that delineates between stable and unstable rock masses. In the Southern Alps, tectonic forces have pervasively fractured intrinsically weak rock to the verge of instability, such that the entire rock mass is susceptible to failure and landslides can potentially extend to great depths. Conversely, in Fiordland, tectonic fracturing of the strong intact rock has produced fracture densities less than the regional stability threshold. Therefore, bedrock failure in Fiordland generally occurs only after geomorphic fracturing has further reduced the rock mass strength. This dependence on geomorphic fracturing limits the depths of bedrock landslides to within this geomorphically weakened zone.

Modelling interactions between fold–thrust belt deformation, foreland flexure and surface mass transport

ABSTRACTInteractions between fold and thrust belt deformation, foreland flexure and surface mass transport are investigated using a newly developed mathematical model incorporating fully dynamic coupling between mechanics and surface processes. The mechanical model is two dimensional (plane strain) and includes an elasto‐visco‐plastic rheology. The evolving model is flexurally compensated using an elastic beam formulation. Erosion and deposition at the surface are treated in a simple manner using a linear diffusion equation. The model is solved with the finite element method using a Lagrangian scheme with marker particles. Because the model is particle based, it enables straightforward tracking of stratigraphy and exhumation paths and it can sustain very large strain. It is thus ideally suited to study deformation, erosion and sedimentation in fold–thrust belts and foreland basins.The model is used to investigate how fold–thrust deformation and foreland basin development is influenced by the non‐dimensional parameter , which can be interpreted as the ratio of the deformation time scale to the time scale for surface processes. Large values of imply that the rate of surface mass transport is significantly greater than the rate of deformation. When , the rates of surface processes are so slow that one observes a classic propagating fold–thrust belt with well‐developed wedge top basins and a largely underfilled foreland flexural depression. Increasing causes (1) deposition to shift progressively from the wedge top into the foredeep, which deepens and may eventually become filled, (2) widespread exhumation of the fold–thrust belt, (3) reduced rates of frontal thrust propagation and possible attainment of a steady‐state orogen width and (4) change in the style and dynamics of deformation. Together, these effects indicate that erosion and sedimentation, rather than passively responding to tectonics, play an active and dynamic role in the development of fold–thrust belts and foreland basins. Results demonstrate that regional differences in the relative rates of surface processes (e.g. because of different climatic settings) may lead to fold–thrust belts and foreland basins with markedly different characteristics. Results also imply that variations in the efficiency of surface processes through time (e.g., because of climate change or the emergence of orogens above sea level) may cause major temporal changes in orogen and basin dynamics.