Gravel Placement Research Articles

Separating impacts of storm characteristics and mitigation activities on suspended sediment: Implications for sampling to evaluate mitigation success

Mitigation activities are often implemented to reduce anthropogenic sediment loads to sensitive ecosystems, including coral reefs, but effectiveness is rarely documented due to a lack of pre-mitigation data and to the difficulty of separating the impacts of mitigation from those of storm size and intra- and inter-storm variability. Here we present a method using stormwise metrics to quantify the effectiveness of a sediment mitigation project in American Samoa, where an aggregate quarry covering <1 % of a small watershed (drainage area 1.8 km2) generated approximately half of the annual suspended sediment load to the coast. Rainfall, runoff, turbidity and suspended sediment concentrations (SSC, mg L–1), yield (SSY, tons km−2 per unit time) and loads (SSL, tons per unit time) were monitored periodically over a five-year period upstream and downstream of the quarry. Mitigation included revegetation and placement of gravel on roads and processing platforms followed by installation of retention ponds. Storms were identified using automated storm separation, and a simple regression model using maximum area-normalized storm discharge (Qmax) estimated SSC, SSY and SSL for each mitigation stage (post-gravel, post-ponds) for a reference storm sequence. Regression parameters, and SSL and SSC for the reference storm sequence were calculated for a range of storm separation parameters. Monte Carlo sampling of the regression errors was used to calculate a mean and standard deviation of SSL and its change following mitigation. SSC was nearly 100x higher during large storms than during small storms, demonstrating the need to account for storm size to detect impacts of mitigation. After mitigation, SSL downstream of the quarry decreased by 63–82 % for all storms and by 88–92 % for small storms, and SSY downstream of the quarry was similar to SSY from the forested watershed upstream. Mitigation of sediment loads can target a small fraction of a watershed area that accounts for the majority of the human impact. Combining stormwise metrics with simple regression modeling and uncertainty analysis is a simple and novel way to detect and quantify the effectiveness of mitigation activities on sediment loads.

Concurrent 10. Presentation for: Collaborating to bring new technology on developments

Presented on Wednesday 18 May: Session 10 Project delivery certainty is a key a success factor for positive business outcomes. Taking on world first applications across multiple delivery streams comes with risk that requires significant risk reduction to meeting business requirements. The Julimar Development completed this successfully across both drilling and completions, and subsea. Reliable multizone completions with robust sand control have traditionally been a challenge in high-rate gas wells. Cased hole stacked gravel packs can leave high mechanical skin, require multiple trips and are complex operations. While Open Hole Gravel Packs (OHGPs) have provided reliable sand control in such wells, multizone applications have been limited due to the tradeoff between effective gravel placement and zonal isolation. Recent developments in technology have enabled reliable gravel placement and complete zonal isolation. The collaboration between Woodside and Subsea 7 has delivered an ‘industry first’ on the Julimar Project, with the completion of an 18″ Corrosion-Resistant Alloy (CRA) gas transmission flowline installed via reel-lay – the largest diameter insulated CRA pipeline ever reeled. For background, most projects have traditionally used the ‘S-Lay’ method for installing pipe in Australia – the reel-lay method is less common. A key benefit of the reel-lay method is it removes thousands of welds from the offshore installation vessel critical path, transferring them onshore into a safer, quality-controlled environment earlier in the schedule. Pipe joints are welded into ‘stalks’ which are then spooled onto purpose-built reel-lay vessels. Woodside and Subsea 7 were able to jointly demonstrate the safety, quality, technical and cost advantages of this innovative but field-proven reeled pipe-lay technology. The 18″ CRA flowline is a tangible example of the performance that can be delivered through early collaborative engagement and strategic investment in technology and is a step change in Australia and the industry. This joint presentation discusses contracting, design, execution and evaluation of technologies on the Julimar Development. It includes the method followed for reel-lay technology selection, engineering development, post project evaluation and the health and safety benefits. The presentation provides both the Operator and Contractor perspectives on the challenges of implementing new technology in developments in Australia. To access the presentation click the link on the right. To read the full paper click here and also here.

Multiple world first technology applications on Julimar Development Phase 2 – multizone openhole gravel packing with enhanced shunted screens and zonal isolation in high rate gas wells and 18″ reel lay for corrosion resistant alloy (CRA) flowlines

Project delivery certainty is a key success factor for positive business outcomes. Taking on world first applications across multiple delivery streams comes with risk that requires significant risk reduction to meet business requirements. The Julimar Development completed this successfully across both drilling and completions, and subsea. Reliable multizone completions with robust sand control have traditionally been a challenge in high-rate gas wells. Cased hole stacked gravel packs can leave high mechanical skin, require multiple trips and are complex operations. While OpenHole Gravel Packs (OHGPs) have provided reliable sand control in such wells, multizone applications have been limited due to the trade-off between effective gravel placement and zonal isolation. Recent developments in technology have enabled reliable gravel placement and complete zonal isolation. The largest flow line installation by reel lay for corrosion resistant alloy (CRA) flowlines was previously 16″. Increasing this size to 18″ required an in-depth understanding of key risks for the contractor to deliver on the size increase, and for Operator to engineer in risk mitigation. Key areas to understand included vessel capability, new build spool base, engineering methods to support delivery and the Operators role in change management when additional risks are identified, or issues occur. This paper discusses contracting, design, execution and evaluation of technologies on the Julimar Development. It includes methodology followed for both technology selections, engineering development, qualification tests, post project evaluation, lessons learned along with health and safety benefits.

Collaborating to bring new technology on developments

Project delivery certainty is a key a success factor for positive business outcomes. Taking on world first applications across multiple delivery streams comes with risk that requires significant risk reduction to meeting business requirements. The Julimar Development completed this successfully across both drilling and completions, and subsea. Reliable multizone completions with robust sand control have traditionally been a challenge in high-rate gas wells. Cased hole stacked gravel packs can leave high mechanical skin, require multiple trips and are complex operations. While Open Hole Gravel Packs (OHGPs) have provided reliable sand control in such wells, multizone applications have been limited due to the tradeoff between effective gravel placement and zonal isolation. Recent developments in technology have enabled reliable gravel placement and complete zonal isolation. The collaboration between Woodside and Subsea 7 has delivered an ‘industry first’ on the Julimar Project, with the completion of an 18″ Corrosion-Resistant Alloy (CRA) gas transmission flowline installed via reel-lay – the largest diameter insulated CRA pipeline ever reeled. For background, most projects have traditionally used the ‘S-Lay’ method for installing pipe in Australia – the reel-lay method is less common. A key benefit of the reel-lay method is it removes thousands of welds from the offshore installation vessel critical path, transferring them onshore into a safer, quality-controlled environment earlier in the schedule. Pipe joints are welded into ‘stalks’ which are then spooled onto purpose-built reel-lay vessels. Woodside and Subsea 7 were able to jointly demonstrate the safety, quality, technical and cost advantages of this innovative but field-proven reeled pipe-lay technology. The 18″ CRA flowline is a tangible example of the performance that can be delivered through early collaborative engagement and strategic investment in technology and is a step change in Australia and the industry. This joint presentation discusses contracting, design, execution and evaluation of technologies on the Julimar Development. It includes the method followed for reel-lay technology selection, engineering development, post project evaluation and the health and safety benefits. The presentation provides both the Operator and Contractor perspectives on the challenges of implementing new technology in developments in Australia.

Suitability and sustainability of spawning gravel placement in degraded river reaches, Belgium

Restoring in-stream spawning habitats in degraded rivers has received increasing attention as a tool for mitigating local wild fish population declines, notably in response to the European Water Framework Directive (WFD). However, spawning gravel placements are far too often designed without accurate knowledge of the morphodynamic river processes, resulting in a limited efficacy and longevity of the artificial spawning ground. To address the combined effects of bedload transport and fine sediment clogging processes on the sustainability of artificial spawning gravel habitats, we examined the effects of such rehabilitation actions on six degraded river reaches in Wallonia, Belgium. The monitoring scheme was based on the evolution of the thickness and clogging of the spawning gravel (using wooden stakes driven into the gravel layer to measure the depth of the anoxia) and on the PIT-tagged tracking of gravel dispersion over a period of 3.6–8.5 yrs. On the one hand, the results highlighted that several artificial spawning grounds were quickly clogged because of improper sizing of the spawning material. Gravel that was too coarse to be mobilized by the river and that had a narrow grain size range favoured fine sediment accumulation within the interstices of the gravel layer. On the other hand, one spawning gravel placement was rapidly scoured (after 2.2 yrs) because of an undersizing of the gravel with respect to flow competence. In the end, one gravel placement presented adequate gravel sizing, allowing periodic gravel transport over short distances (the mean annual travel distance was ~3 m). The longevity of a gravel placement and the ability of the displaced gravel to form new spawning grounds downstream were strongly dependent on the distance that the placed gravel was likely to travel, which in turn depended on several hydromorphological parameters, such as unit stream power, channel morphology and bed texture. The key parameters highlighted in this study need to be acknowledged when designing spawning gravel placement projects.

Ecological functions of restored gravel bars, the Trinity River, California

Gravel augmentation has been increasingly used in sediment-limited systems in regulated channels as a means of creating morphological changes that beneficially affect the functioning of downstream ecosystems. Despite this trend, there have been few empirical studies to quantify these effects in relation to the morphology of gravel bars, especially in terms of riverine material exchanges such as heat and organic matter. We conducted field-based hydro-geomorphological observation of different mechanisms of gravel bar restoration in the downstream of Trinity Dam, California: a medial and a point bar deposited fluvially during high-flow gravel injection, an additional point bar created by direct placement of gravel, and an island created by side channel excavation. We measured water temperature, suspended particulate organic matter (S-POM) concentration, hydraulic gradients and shallow water width under base flow conditions along the perimeter of the gravel features. We then assessed water temperature modulation derived from hyporheic exchanges and S-POM retention of the gravel features, comparing the functions of the dynamically-constructed medial and point bars to those of the mechanically-constructed island and point bar. Diurnal water temperature fluctuations showed a notable thermal heterogeneity including cooling (1.5–3.1 °C) during summer peak temperatures, buffering in amplitude (1.2–4.0 °C) and lagging in phase (0.3–14.5 h), especially in the bar-tails and alcoves of the gravel bars. All of the gravel features reduced S-POM concentration at baseflow, showing the highest retention efficiency in the medial bar. In addition, the fluvially formed the medial and point bars had higher hydraulic gradients and wider shallow waters than the constructed features. Our results indicate that gravel bar restoration can increase hyporheic exchange and S-POM retention by increasing hydraulic gradients at baseflow, refreshing bed materials to enhance substrate permeability, and elongating the wetted boundary length in shallow waters. Our study results suggest that mechanically created in-channel geomorphic features combined with coarse sediment augmentation can increase channel complexity, driving hyporheic flows and increasing S-POM retention, thus ultimately resulting in thermal heterogeneity and food availability along gravel bed channels.

Deepwater Gas-Zone Shutoffs With Wireline in Openhole-Gravel-Pack Completions

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 170789, “Deepwater Gas-Zone Shutoffs With Wireline in Openhole- Gravel-Pack Completions,” by Claudia Zettner, Hank Bensmiller, and Tom Lane, ExxonMobil, prepared for the 2014 SPE Annual Technical Conference and Exhibition, Amsterdam, 27–29 October. The paper has not been peer reviewed. An operator successfully executed two wireline through-tubing gas-shutoff (GSO) workovers in high-angle openhole-gravel-pack (OHGP) completions to isolate high-gas/ oil-ratio (HGOR) zones, resulting in significantly increased oil production. This paper summarizes the GSO concept, completion modeling, job planning, completion-equipment testing, job execution, and production results from one of these two wells (the processes and results associated with the second well are detailed in the complete paper). Introduction All producers in the field of study were drilled from a 36-slot tension-leg platform (TLP) at a water depth of just over 1000 m. OHGPs are the preferred completion option in this field. It was recognized during the project-design phase that controlling unwanted gas and water in the future would be challenging. The well-work solution proposed and described in this paper can address that challenge by providing lower-GOR oil and additional reserves recovery. Although the long-term depletion plans for most reservoirs in the field rely on waterflooding, some producing reservoirs have been used to store surplus gas until gas-export facilities were operational. As these injected gas caps expanded toward producers, GORs increased to the point at which processing facilities were gas constrained. Producer-well seriatims made on the basis of GOR are used to optimize oil production. The highest- GOR wells are typically cycled to manage GORs and then shut in when cycling is no longer effective. Engineering principles and field experience have shown that gas breakthrough in any zone in a well can affect overall production significantly. High gas mobility, coupled with good injection support in the gas-producing interval, can result in an HGOR, and thus a noncompetitive, producer. The completion diagram in Fig. 1 illustrates the general design of the lower completion. External shunt tubes prevented external casing packers (ECPs) on early wells. Later wells have internal shunt tubes that allow ECPs in the gravel-packed section of the well. Completions include gravel packs to minimize sand production from the unconsolidated reservoirs. Gravel-pack screens are shunted to help ensure gravel is transported and placed along the length of the screen. Gravel placement is generally effective, and sand production is rarely a problem in this field. Oil producers are directionally drilled because most reservoir objectives are not directly underneath the TLP. Reservoir penetrations are often at a high angle from vertical to provide the permeability thickness necessary to deliver target rates.

Juvenile Salmonid Utilization of Floodplain Rearing Habitat After Gravel Augmentation in a Regulated River

Gravel augmentation is used in sediment-starved streams to improve salmonid spawning habitat. As gravel is added to river channels, water surface elevations may rise in adjacent areas, activating floodplain habitat at lower flows, and floodplains inundate more frequently, potentially affecting the quantity and quality of juvenile salmonid rearing habitat. We analysed 5 years of juvenile Chinook salmon Oncorhynchus tschawytscha and steelhead Oncorhynchus mykiss data from snorkel surveys before and after gravel augmentation in the Lower American River, a low-gradient, highly regulated alluvial river in California's Central Valley. We measured the quality and quantity of rearing habitat (current velocity and areal extent of inundated riparian vegetation) following gravel placement and tested whether these factors affected juvenile abundance. Gravel augmentation increased floodplain extent by 3.7–19.8%, decreased average flow velocity from 1.6 to 0.3 m s−1 and increased the amount of vegetative cover from 0.3% to 22.6%. Juvenile abundances increased significantly for both species following augmentation. However, the strength of the relationship between abundance and habitat variables was greater for smaller salmonids. These results suggest that, in addition to enhancing salmonid spawning habitat, gravel augmentation can improve rearing habitat where channel incision and/or regulated hydrographs disconnect floodplains from main river channels. Copyright © 2015 John Wiley & Sons, Ltd.

Effective Perforating and Gravel Placement: Key to Low-Skin, Sand-Free Production in Gravel Packs

Summary Cased-hole gravel packing is commonly used to control sand production from oil and gas wells. The success of a cased-hole gravel-pack job depends on the ability to effectively pack perforation tunnels, which act as conduits between the reservoir and the wellbore for hydrocarbon production. This project presents a systematic approach for removal of perforation damage, effective gravel placement, and packing of the perforation tunnels. It was found that dynamic underbalanced perforating (DUP) greatly increased the ability to pack the perforation tunnels and improved the connectivity to the reservoir. Guidelines to DUP and executing the perforation-packing job are presented. This study also discusses the current practices commonly employed in cased-hole gravel packing to pack perforation tunnels and the potential limitations of these practices. Incomplete packing of perforation tunnels is mostly encountered in gravel-pack jobs completed with brine as the carrier fluid (water packs). The proposed technique involves DUP before the gravel-pack operation, followed by pumping the gravel slugs in a nondamaging carrier fluid in concentrations ranging from 1 to 3 lbm of proppant added per gallon of fluid (ppa). These slugs range from 5 to 7 bbl and are pumped intermittently between stages of the completion fluid to minimize cost. The carrier fluid, by virtue of its viscosity and mechanical suspension capability, ensures that the gravel enters the perforations. This technique was implemented successfully at the Abu Cluster field in west Malaysia. This reservoir had extremely high permeability (1.5 to 3 darcies), with sand production a major concern. Several jobs were completed with the previously mentioned technique, and perforation-packing factors improved from 8 to 38 lbm of gravel per foot of perforations. Discussion of the placement and production data is presented. Sand-free production has been achieved with reduced drawdown across the sandface. The results show a linear relationship between pack factor and normalized productivity index (PI), indicating that gravel-packed perforations improve well productivity.

Effective Perforating and Gravel Placement: Key to Sand-Free Production

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper IPTC 12581, "Effective Perforating and Gravel Placement: Key to Low-Skin, Sand-Free Production in Gravel Packs," by Samyak Jain, SPE, Raymond Tibbles, SPE, and Jock Munro, Schlumberger, and Rajeswary Suppiah and Norhisham Safin, SPE, Petronas Carigali, originally prepared for the 2008 International Petroleum Technology Conference, Kuala Lumpur, 3-5 December. The paper has not been peer reviewed. Cased-hole gravel packing is used to control sand production from oil and gas wells. The success of a cased-hole gravel-pack job depends on the ability to pack perforation tunnels effectively. The full-length paper presents a systematic approach for perforation-damage removal, effective gravel placement, and packing of the perforation tunnels. Guidelines to surging the formation and executing the perforation-packing job are presented. Introduction Every year the petroleum industry spends USD millions cleaning sand out of wells and repairing problems related to sand production, and it loses additional dollars by restricted production rates. Sand production is a common occurrence in highly unconsolidated formations. In cased-hole applications, perforations act as a conduit for fluid flow between the formation and the wellbore. Production rates can be reduced severely if the packed perforations are damaged. The ability of the well to deliver its potential productivity depends on the inflow area these perforations provide for fluid flow. Perforations may be dam-aged for a number of reasons including perforation debris, a compacted or crushed zone consisting of pulverized sand grains, perforations filled with reservoir sand, and other drilling- and completion-related activities. Background Perforation Surging. Perforating is the critical process connecting the reservoir with the wellbore. The selection of the gun system is driven by many factors including wellbore dimensions and formation and reservoir properties. One of the most critical parameters for perforation strategy is the rock strength, measured as unconfined compressive strength. It is recognized throughout the industry that for sand-control completions, both high shot density and big-hole charges are the optimum gun/charge configuration. Increased area open to flow maximizes the productivity of the well while it reduces the fluid velocity per perforation, reducing the risk of sand production through the gravel pack and sand screens. High-velocity flow through isolated perforations can create "hot spots" that, with time, can erode through the screens, resulting in massive sand production and sometimes the loss of the zone or the well.

Factors Affecting Horizontal Well Gravel Pack Efficiency

Abstract Four major factors affecting horizontal well gravel pack were studied using a 3D simulator developed for horizontal well gravel packing. The factors included settling effect, gravel concentration, injection rate and carrier fluid viscosity. Three actual field horizontal well gravel pack jobs obtained from the literature were performed using the simulator to study these factors. The effect of carrier fluid viscosity on gravel pack efficiency was studied by varying the viscosity between 1 and 51 cP, injection rate between 0.159 and 0.636 m3/min and gravel concentration between 0.50 and 4.0 pound mass per gallon. Simulation results demonstrate the validity of the solution routine and the capability of the simulator, because the results were in agreement with the field results. The predicted pack efficiency for cases that considered settling effect are consistently higher than the cases without settling effect. The study also showed that the settling factor decreases with increasing gravel concentration and injection rate. Introduction Several authors have investigated the factors affecting gravel transportation and placement towards achieving an effective gravel pack. Gruesbeck et al.(1) performed experiments to measure pack efficiency as a function of screen parameter, fluid and gravel properties, completion configuration and angle of inclination of the wellbore. They concluded that packing efficiency increases with lower gravel concentration, lower gravel density, higher flow rate and increasing resistance to fluid flow in the tailpipe/screen annulus. Hodge(2) substantiated Gruesbeck et al.'s work by determining the accuracy of the predicted equilibrium bank height. Elson et al.(3) reported a study conducted to define optimum gravel pack procedures and completion design factors for high angle wells. Results of the study showed that high viscosity carrier fluids with high gravel concentration provide good gravel transport, but are unsuitable in wells with angles of 80 º from vertical. Skaggs(4) presented the results of a large-scale vertical wellbore model he used to study gravel transport through perforations during a high-density squeeze gravel packing operation. He concluded that the transport efficiency through perforations increases with increased fluid viscosity, gravel concentration and annular velocity. Winterfeld and Schroeder(5) developed a finite element numerical simulator and used it with a full-scale wellbore model to study gravel placement in perforations and annulus. Their model was based on mass and momentum conservation equations, as well as those for vertical wells. Peden et al.(6) developed some mathematical design models for predicting the optimum combination ofrequired design parameters, such as tailpipe diameter, slurry flow rate and gravel concentration, for an optimum packing efficiency. These models were based on extensive experimental study of factors affecting packing efficiency and dimensional analysis of obtained data. In 1988, Wahlmeier and Andrews(7) improved on the earlier works of Gruesbeck et al. and Peden et al. by developing a pseudo-three-dimensional mathematical model suitable for designing and evaluating gravel pack treatments. Shryock(8) worked on a full-scale deviated model and had similar conclusions with earlier works.

Technology Update: Modeling Advances ER Openhole Horizontal Gravel Packing

Advances in drilling technology are producing record-breaking extended-reach (ER) wells. The record for displacement from a floating installation has been pushed beyond 24,500 ft, and horizontal completions longer than 6,500 ft have become commonplace. Well-completion technology is also evolving. To facilitate cost-effective well-construction programs, completions engineers are increasingly exploring materials science and incorporating computational/numerical-modeling techniques to anticipate induced material deformations from ER processes. Sand-Screen Deployment Many ER wells are openhole completions requiring sand management to guarantee trouble-free, interventionless production. Therefore, it is necessary to address the problem of sand-screen deployment and gravel placement. In considering screen deployment, drag force on the screen must be analyzed. Greater well displacements imply higher total drag force. This force may become larger than the downward force available from the string weight, preventing the sand screen from reaching the required depth. Drag may also physically damage the sand screen. Reducing the drag force requires stronger, lighter screens and low-drag fluids. Counteracting the drag forces exerted on openhole wells requires stronger, lighter screens and low-drag fluids. Meanwhile, circulating gravel packs are subject to the limitations of fluid frictional pressure loss during gravel placement vs. increased fluid leakoff and the fracture pressure of the exposed reservoir. Placement fluids with low hydraulic frictional pressure loss are one avenue for study. Lightweight gravels requiring lower circulating rate for placement—and hence inducing lower friction pressures—are another. Deepwater ER wells, in particular, are a significant challenge. These wells often have excessive fluid loss, variations in hole stability and hole geometry, and/or an extremely narrow window between bottomhole pressure and fracture gradient. The narrow pressure window, in particular, can be a significant concern because high pump rates required for long-distance proppant transport may fracture the formation, causing fluid loss and a sand bridge or early screenout during gravel placement. The pumping boundaries for openhole gravel packing are Qmin, the rate at which a sand bridge is likely to form (typically considered to be a dune ratio of 85%), and Qmax, the rate that would result in formation fracturing pressure. Critical rates occur in washed-out hole sections and at extreme displacements, where Qmin can exceed Qmax. Therefore, reducing Qmin is a critical element in planning a long, ER openhole gravel-packing operation. An ideal solution is to use the low settling velocities of reduced-density gravels. The issues affecting the suitability of these new materials are the main theme of this article. Conventional gravels used for sand control have been sized natural sands and manufactured ceramics. The specific gravity (sg) of these materials varies between 2.65 and 2.71. For a typical wellbore configuration with an 8½-in. open hole, the ideal placement rate would be approximately 9.5 bbl/min, generating friction pressure greater than 5,000 psi in a borehole length of 5,000 ft. This additional pressure on the formation is generally well above the fracture pressure and would result in an aborted gravel-pack attempt.

Use of Viscoelastic Surfactant-Based Diverting Agents for Acid Stimulation: Case Histories in GOM

Summary Viscoelastic-surfactant (VES) -based diverting products have been used successfully in matrix acidizing in the Gulf of Mexico (GOM) in recent years. The uses of VES diverters range from remedial matrix-acid or nonacid-cleanup treatments to use before gravel- or frac-packing operations to clean up long intervals after perforating. Success or failure of these treatments is often related to the efficiency of diverting agents, especially for acid treatments on wells with long, heterogeneous intervals or multiple-zone completions. A VES diverting agent is of particular interest to remedial treatments of frac-/gravel-packed wells, because damage to the near-wellbore area and completion should be minimized for optimum production. Laboratory studies and field applications have demonstrated the nondamaging properties of a VES fluid. This paper reviews the properties of the vesicular-type VES diverting fluid, reviews the operational considerations, and presents several case histories with VES diverting agents in the GOM. The bottomhole static temperatures (BHSTs) of these cases range from 140 to 290°F for both gas and oil wells. With an internal breaker system, the diverter does not require contact with formation fluid, brine, or acid to clean up and provide optimum production. In some cases, as many as four stages of diverters were pumped in the treatment, and successful diversion was observed for each stage. The paper outlines field-operational considerations and detailed fluid properties, which were tailored to specific well conditions and formation characteristics. Details and pressure responses of the treatments are discussed. Introduction Matrix-acid stimulation has been frequently used in the GOM to remove formation damage caused by drilling-mud invasion, clay swelling and clay migration, and production impairment from inorganic scaling. When acid is injected into the reservoir below the fracturing rate and pressure, acid will typically enter the region with the highest permeability. Proper diversion is required to direct the treatment fluid into the damaged zone to achieve maximum benefit of the acid stimulation. Another area that employs acid treatment in the GOM completions is damage removal before gravel packs or frac packs. Gravel packing has been extensively used as a standard sand-control treatment in the GOM for several decades. Before or after the placement of gravel with completion fluids, low-density brines, or linear gels, an acid treatment is usually pumped to remove the near-wellbore formation damage or high skins encountered in wells perforated overbalanced (Unneland and Waage 1996; Matherne and Hall 1996). In other cases, a clay-acid package is often pumped into the formation before the gravel pack to stabilize the residual clays. The effectiveness of these treatments is often directly related to the ability of the acid treatment to remove the near-wellbore damage and connect the wellbore to the formation. In addition to determining the most effective combination of acid blends and volumes for each particular reservoir, treatment design and planning are done to ensure that the correct procedure is followed to place the acid across the entire interval. Staging of the treatment is used to force acid across the entire interval, treating the damaged portion of the completion. The successful acid placement in matrix treatments of openhole horizontal wells are even more difficult because of the length of the zone treated and potential variation of the formation properties. A successful diversion technique is critical to place the acid at the location where damage exists. A variety of diversion techniques have been practiced in acid stimulations (Rae and di Lullo 2003). Diversion sometimes can be achieved by simply increasing pumping rate during the acid treatment. Viscous diversion techniques such as hydroxyethyl cellulous (HEC) gelled brine and nitrogen foam are often used, especially when the temperature of the well is not very high. Other materials used as an acid-diverting agent include acid-insoluble particulates. A mechanic method such as a ball sealer also has been successful when it is practical. Most of these methods have some limitation to their application, especially in a completion with a sand-control method installed. VES-based diverting products have been developed and widely used in recent years, and their use has found application beyond the limitations of the previously mentioned techniques.

Gravel Packing Long Horizontal Wells With Low Fracture Gradients

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 96396, "The Dynamic Bottomhole Pressure Management: A Necessity to Gravel Packing Long Horizontal Wells With Low Fracture Gradients," by Z. Chen, SPE, and R.J. Novotny, SPE, BJ Services Co., prepared for the 2005 SPE Annual Technical Conference and Exhibition, Dallas, 9–12 October. Unconsolidated formations are commonly found in offshore reservoirs where long and ultralong horizontal wells are required to produce heavy oil economically. Gravel packing is an efficient and cost-effective sand-control practice for these high-permeability, large-porosity, low-fracture-gradient formations. Successful placement of the gravel-pack completion requires that these low-fracture-gradient wells not be fractured during gravel placement. A dynamic-pressure-management scheme is critical to maintain bottomhole pressures (BHPs) in the required range. Introduction Horizontal-well openhole screen completions have been performed for years and offer many advantages. These advantages can be offset quickly by failure if the job is not carefully designed and executed. This is especially the case for wells with long and ultralong horizontal wellbore sections in unconsolidated formations with low fracture gradients. Although horizontal openhole gravel-pack completions have continued to gain acceptance as reliable completion techniques, they are still under development and often encounter new challenges. In some cases, there may not be any safe operational windows under conventional operation procedures. Dynamic BHP Management During gravel placement in horizontal wells, BHP must be monitored constantly to avoid fracturing the formation. Any excessive leakoff will cause a screenout and, thus, an incomplete sand-control completion. To ensure a successful packing job, an effective BHP-management scheme needs to consider both job-design time and actual job execution. Gravel-Packing Model The gravel-packing physical phenomenon in a horizontal well can be described as alpha-/beta-wave packing. Several flow patterns can be encountered in a given section, affecting the pressure-gradient/flow-rate relation. During alpha-/beta-wave packing, a stationary bed is created at the bottom of the flow path and a heterogeneous mixture of solid particles and carrier fluid flows through the upper part (Fig. 1). The stationary bed at the bottom of the flow path builds up and grows forward like a wave; it is from this that the expression "alpha wave" is derived. The flow path or void above the alpha wave will be packed after the alpha wave packs forward to the bottom of the screen. In the alpha-/beta-wave model, it is assumed that the space above the alpha wave will be packed backward to the top of the screen. The packing process during this phase exhibits a pistonlike movement, packing all the space backward, and is named the beta wave (Fig. 2).

Evaluation of a Spawning Habitat Enhancement Site for Chinook Salmon in a Regulated California River

AbstractAn evaluation of the effectiveness of a project to enhance spawning habitat for Chinook salmon Oncorhynchus tshawytscha was conducted in the Mokelumne River, a regulated stream in California's Central Valley. Approximately 976 m3 of clean river gravel (25–150 mm) was placed in berm and gravel bar configurations along the 45‐m enhancement site. Physical measurements taken before and after gravel placement indicate that the project significantly increased channel water velocities, intergravel permeability, and dissolved oxygen; reduced channel depths; and equilibrated intergravel and ambient river temperatures. These positive benefits remained throughout the 30‐month monitoring period. Adult Chinook salmon began spawning at the previously unused site within 2 months after gravel placement and continued to use the site during the three spawning seasons encompassed by the study. Bed material movement was documented by channel bathymetry surveys over two water years. Topographical channel surveys provide a useful tool for monitoring bed material transport and layering redd locations on contour maps. Although its usefulness in restoring salmon populations is poorly understood, gravel enhancement can be an effective means for improving salmon spawning habitat in rivers where upstream dams have effected low gravel recruitment.

Development of the Alba Field—Evolution of Completion Practices, Part 2: Openhole Completions, Conventional Gravel Packing After Drilling With SOBM

Summary Chevron has been successfully drilling and gravel packing openhole horizontal wells in the Alba field (central North Sea) since 1998, and 13 openhole gravel-packed (OHGP) wells drilled with water-based mud (WBM) are currently in production with no history of sand production. Although these wells have been hugely successful with significant net present value (NPV) returns, it was recognized that the future, mature redrill and infill targets cannot sustain the current costs associated with traditional OHGP completions. The challenge was to develop alternative techniques to maintain the benefits of OHGP wells but to achieve a low-cost well and completion concept to assist in realizing new drilling opportunities. Drilling the shale above the top of the reservoir and the productive interval in a single hole section would require removing conventional requirements for setting an additional casing string and changing over to a water-based system before drilling into the reservoir. This would save costs but raises a question concerning the gravel-packing operation. Hitherto, attempts to gravel pack that involve alpha/beta placement techniques using an aqueous carrier fluid following drilling with oil-based systems have had only limited success. The prospective problems were examined by extensive laboratory tests carried out cooperatively by Baroid and Chevron. A new, synthetic oil-based mud (SOBM) formulation was developed, and compatible displacement fluids and procedures were devised. Based on this work, 1,500 ft of shale and reservoir were drilled, a liner that was predrilled over the reservoir section was installed, and screen was run inside the liner. Gravel was pumped using brine as the carrier fluid, and complete gravel placement was achieved. The well has achieved productivity levels at least as good as existing WBM wells. A second well completed in the same manner has given a similar performance. This combination of a liner system and SOBM fluids offers several advantages. There is the prospect of considerable savings with respect to operating time, cementing, and drilling fluids. The liner also gives protection to the screen. This new approach, which represents potential large savings in costs and excellent productivity, is considered applicable to other types of completions when it is desirable to drill with oil-based mud even though conventional thinking would have called for water-based drill-in fluid. This consideration applies to targets in the Alba field and worldwide.

Analysis of Post-Audits for Gulf of Mexico Gravel-Packed Oilwell Completions Leads to Continuous Improvement in Completion Practices

Summary Final production rate alone is not an adequate measure of the success of a well completion. Rather, we must estimate the "po-tential" of a reservoir and judge the ultimate success of a completion on how close we come to achieving this potential. Specific productivity indexes (SPI's) [(BFPD/ft)/psi], specific injectivity indexes (SII'S) [(BFPD/ft)/psi], and completion efficiencies (CE's) (percent of Darcy radial flow) can be calculated at various times throughout a well completion. Analysis of these data quantifies the efficiency of the completion after each individual completion operation, allowing a determination of the effects of each completion practice to be made. In addition to completion efficiency data, a comparison of gravel placement volumes behind casing helps quantify optimum gravel packing procedures. Twenty-two Gulf of Mexico completions have been analyzed using this technique. In this paper we will give details of the results of this analysis, in particular the productivity effects of various methods of underbalanced perforating, gravel packing, and well control. Items of discussion include the effects of underbalanced perforating on well performance, the effects of flowback after perforating on perforation tunnel cleaning, productivity impacts of various types of well control methods following perforating and gravel packing, and comparisons of gravel pack design parameters and gravel placement behind casing.

Gravel Placement in Horizontal Wells

Summary Long, horizontal gravel packs are viable completions that have been placed successfully in more than 80 wells. Extensive field-scale testing has significantly aided the development of field procedures and operating guidelines. Software has also been developed to assist with horizontal gravel-pack design. To be performed properly, these completions require a systems approach for their implementation because drilling and displacing the completion interval, maintaining hole stability, selecting and running equipment, and maintaining returns during the gravel-packing operation must be integrated into the completion strategy. Field experience suggests that, in some cases, gravel packs maintain productivity better than prepacked screens or slotted liners.

Results From the Heidrun Field Cased-Hole Gravel Packs

Summary During the initial phase of the Heidrun field development, five wells were precompleted with state-of-the-art cased-hole gravel-packing techniques. The wells were tested and temporarily abandoned, awaiting tieback to the Heidrun tension-leg platform (TLP). This paper describes the completion techniques applied and presents results of an evaluation of gravel-pack efficiency for the wells. Flow and buildup tests were carried out on the semisubmersible drilling rig before and after gravel packing to evaluate initial productivity. Stabilized well-test data acquired on the Heidrun TLP at full production are presented to document ultimate completion performance for each well. Innovations Perforating with tubing-conveyed perforating guns on a drillstem-test (DST) string allowed perforating, perforation cleanup and flowback, pre-gravel-pack testing, and gravel prepacking to be performed in a single run. A unique loss-control-material (LCM) formula was developed and applied to control fluid losses to the formation. Prepack modeling and alternating stages of clear brine and slurry were used to optimize gravel placement. A temporary-abandonment system was developed and installed that used a weight-actuated ball valve to abandon the well temporarily without placing any damaging fluids across the production zone. Gravel-pack screen assemblies included alternative-path gravel placement with four shunt tubes per gravel-pack screen assembly. The innovative gravel-packing techniques used at Heidrun resulted in high completion productivity and correspondingly high flow rates. A study performed to evaluate the economic impact of acceleration showed that going from a 20,000- to a 30,000-BOPD well rate added $108 million in pretax net present value to Heidrun project economics. Actual results will be greater because well rates have exceeded 43,000 BOPD. Introduction The Heidrun field lies 120 miles offshore mid-Norway in the Haltenbanken area in approximately 1,140 ft of water in the Norwegian Sea. Hydrocarbons were proven in three main reservoirs of Jurassic age: the Middle Jurassic Fangst group and the Lower Jurassic Tilje and Are formations. Fig. 1 provides a type log. The field is being developed from the world's first concrete-hull TLP. Ten wells were predrilled from the main 56-slot template along with six subsea, seawater injection wells drilled from the two four-slot satellite templates. First oil production occurred on Oct. 18, 1995. The Heidrun TLP is currently producing at plateau rate of more than 230,000 BOPD.

Alba Field Cased-Hole Horizontal Gravel Pack: A Team Approach to Design

Summary A 700-ft cased-hole horizontal well was gravel packed and completed in the Alba Field, central North Sea. The completion incorporated a number of new technologies adopted for a horizontal casedhole completion, including both equipment and fluids. The zone was completed in two stages using a horizontal stack-pack approach. Perforation packing was optimized by performing a staged acid prepack with the guns in the hole using a low-density synthetic gravel substitute in a shear thinning carrier fluid. This was a world-first achievement at a cased-hole gravel pack using the stack-pack approach in a horizontal well. A solids-free fluid-loss control material was evaluated and chosen for the high-permeability Alba sands (3 darcies). Extensive lab testing was performed to ensure minimal damage from various fluids. A 30-ft physical model was used to optimize annular pack efficiency. A gravel placement computer simulation was used to design pump rate, sand concentration, and gel loading to optimize annular and perforation-pack efficiency.