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. Introduction Gravel packing is a well-completion technique used to exclude formation sand from produced reservoir fluids and extend completion longevity. It is performed by placing a gravel-retention device (such as a wire-wrapped screen) in a well opposite the completion interval, and subsequently circulating gravel around the gravel-retention device to create a permeable filter. Gravel packing has been applied in vertical and deviated wells that were completed either cased or openhole. Transport fluids used to gravel pack wells have been either polymer-viscosified brines or unviscosified brines. Of the two choices, unviscosified brines are usually preferred because they exhibit lower-porosity, void-free packs. Several authors have investigated the factors affecting gravel placement, productivity, and completion longevity.1–17Fig. 1 illustrates an example of the gravel placement at well deviations of 0 and 45° using water as the transport fluid.16 Note that the gravel is initially placed at the bottom of the well and packs sequentially upwards. At well deviations in excess of 60°, the angle of repose of gravel is exceeded and the gravel initially settles on the low side of the well and remains at rest, unless sufficient flow is available to move it forward. The 60° well deviation represents a transition in the placement of gravel, because at lower well deviations the gravel will settle to the bottom of the well. Placing gravel at the bottom of a highly deviated well requires higher pump rates and a slightly different completion geometry than in vertical wells. A large-diameter wash pipe can be used inside the screen to enhance placement.2 It forces a larger fraction of the fluid to flow along the outside of the screen, rather than being diverted into the screen/wash-pipe annulus. The higher screen-casing annulus flow rate assists in transporting the gravel and prevents a premature stall of the gravel pack before it reaches the bottom of the completion. When the proper screen and wash-pipe size are used, the gravel-deposition process consists of a primary or "alpha" wave that packs from the top to the bottom of the completion, leaving an open void over the gravel dune. Upon reaching the bottom of the completion, a subsequent secondary or "beta" wave deposition proceeds in the opposite direction of the alpha wave (towards the top of the well) until the interval is completely packed. The packing process in a highly deviated well is portrayed in Fig. 2.16 This technology has been used to successfully gravel pack many conventional wells with deviations as high as 80° or more and completion lengths of several hundred feet. Until recently, gravel packing long, horizontal wells has not been used as a completion technique, apparently because the technology was not thought to be in hand. Instead, prepacked screens and slotted liners had been used as stand-alone sand-control equipment, even though their performance in conventional wells had been disappointing. Their improved performance in horizontal wells is probably attributed to much lower flow rates per foot of completion interval than when used in vertical wells. In horizontal service, the initial productivities of screens and slotted liners usually have been good, but their tendency is to plug and restrict productivity, particularly when completed in dirty sands, when high water or gas/oil ratios occur, or when placed in viscous-oil service. Not surprisingly, screens and slotted liners seem to perform best in clean, high-permeability sands. Hence, how well screens and slotted liners perform tends to be site-specific. Gravel packing horizontal wells has been successfully demonstrated in field-scale studies and actual completions. Gravel has been placed in over 80 wells, with intervals ranging from 600 to 3,300 ft. The test data and field experience suggest that packing even longer intervals is possible. The following discussion reviews testing and field experience gained with gravel packing long horizontal wells. It also presents guidelines for completion operations. Field-Scale Testing Most field-scale testing for simulating gravel packs has been performed with clear plastic models. Until recently, the gravel-pack-model lengths were less than 100 ft, and most were about 25 ft long. The implications of testing in these models were that they were too short to provide meaningful results for long, horizontal wells. While numerical simulation was also an alternative, designing completions using unverified simulators was believed to be risky and unreliable. For these reasons, a field-scale model was designed and constructed to simulate gravel packing horizontal wells. Description of the Model. The horizontal model is 1,500-ft long with a 4 1/2-in. outside diameter (OD) [4-in. inside diameter (ID)]. It is equipped with a centralized 2 1/16-in. screen (0.006-in. slot openings). The wash-pipe diameter is 1.315 in. The wash-pipe OD to screen ID ratio is 0.75. The model is equipped with clear, high-strength plastic windows capable of operating at pressures of 1,000 psi to allow the visual observation of the packing process at six locations along its length. Sliding sleeves are also located along the model to allow the visual observation of gravel deposition in the model at that location after pumping has ceased. Fluid loss is simulated with 400 perforation tubes that are l-ft long, 1/2-in. diameter pipe filled with resin-coated 40/60 U.S. mesh gravel. Five pressure sensors are installed at strategic locations. Inlet and exit flowmeters measure entrance and return flow. Pumping is performed with a field unit. Data acquisition consists of recording rates, pressures, and gravel-mix ratio as a function of time. Fig. 3 illustrates a schematic of the model while Figs. 4 and 5 show the windows and the perforation arrangement. On the basis of previous experience, water was chosen as the carrier because viscous fluids have a strong tendency to bridge and dehydrate the gravel prematurely in long, highly deviated wells.16

Long, horizontal gravel packs are viable completions that have been placed successfully in over 20 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 since 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.

This article presents the development of a computational tool to guide horizontal gravel-pack design for long horizontal offshore wells. Mechanistic model hypotheses, experimentation at a largescale flow loop, and software development are detailed. The computer simulation results are then compared with field data collected in the Campos basin operations, offshore Brazil. A discussion on design alternatives for a long horizontal well at low fracturegradient formations is presented. This discussion includes a sensibility analysis on screen eccentricity, open and closed blowoutpreventer (BOP) configurations, and alpha (alone) vs. alpha plus beta wave displacement options.

This article presents the development of a computational tool to guide horizontal gravel pack design for long horizontal offshore wells. Mechanistic model formulation, experimentation at a large scale flow loop and software development are detailed. The computer simulation results are then compared with field data collected in Campos Basin operations, offshore Brazil. A discussion on design alternatives for long horizontal well at low frac gradient formations is presented. This discussion includes a sensibility analysis on screen eccentricity, open and closed BOP configurations and alpha vs alpha plus beta wave displacement options. Introduction Gravel Packing is today the most frequently applied sand control technique in Campos Basin. Due to the critical conditions, such as the deep and ultra deepwater and low frac gradients, a lot of precision is required to assure gravel packing success. Most models available in the industry for horizontal gravel pack design are essentially empirical, resulting in imprecise predictions for extrapolated conditions. The new scenario for offshore development in Brazil includes heavy oil fields in deepwaters where 2000m horizontal sections are required. Sand control options are a major issue and gravel packing is a strong candidate if pressure loss issues can be overcome. These aspects were the main motivators for a research project including theoretical and experimental developments. A mechanistic model to describe the whole operation, including sand injection and alpha/beta waves propagation, fluid leakage, multi zonal isolation and beta wave pressure reduction optimization was developed. The main core of the model, aiming the definition of alpha wave height, is based on a two layer model approach. Initially developed for hydrotransport applications, this kind of model have been adapted by several authors for drilled cuttings transport analysis. It is a consensus among design and operation engineers that a physically based software is a necessary rigsite tool for determining operational parameters, specially when last minute data have to be considered. Several authors present experimental results of horizontal gravel packing performed in test facilities (Forrest1, Penberthy2, Sanders3). In the present study, 15 runs on a full scale displacement loop where the effects of pipe eccentricity, particle diameter, particle shape, fluid flow rate and return flow rate could be quantified. The results allowed the adjustment of fundamental coefficients in the mechanistic model. Theoretical Model The proposed model consists on the following steps: pressure propagation during string injection, alpha wave height calculation, pressure propagation during alpha wave propagation and pressure propagation during beta wave propagation. A brief description of each step follows while more details are highlighted in Martins4et al. Alpha Wave Height Prediction In order to predict alpha wave deposition heights, a two layer model was adopted. The present model is an extension, for horizontal gravel packing applications, of the model proposed by Martins5 for drilled cuttings transport analysis. The following formulation was developed to describe the eccentric horizontal annular flow a solid-Newtonian fluid mixture, aiming the prediction of an equilibrium alpha wave bed height. The solids are characterized by their average diameter and sphericity. The model consists of a stratified two layer configuration which allows, with an unique formulation, the simplified representation of the system in different flow patterns (stationary and moving beds). Fig. 1 shows schematically the proposition.

The objective of this study is to introduce a new neutral wettability proppant that improves flow and cleanup of the proppant pack. It is known that the proppant pack permeability is the primary factor that affects the productivity of a fractured well. In such operations, fracturing fluid (cross-linked or linear) is used to deposit the proppant. In order to transport proppant within the fracture, fracturing fluid rheological properties must be attained based on fracture type, job design metrics, formation characteristics, proppant properties and proppant loading. These fluid properties are typically adjusted by using gelling agents and other chemical additives to ensure transport capability. The types and concentration of gelling agents, cross-linkers, and breakers, are known to affect the permeability of the pack. If these fluids are not removed, they build up in the proppant pack. This fluid retention leads to decreased permeability and reduced effective half-length of the fracture. In this paper a neutral wettability proppant that is neither oil wet nor water wet was used to (1) eliminate capillary pressure within the proppant pack and (2) alter the interaction between aqueous/organic (hydrocarbons) and the proppant surfaces by decreasing the intra-molecular interactions between the fluids and the proppant surfaces thus resulting in improved flow compared to native surfaces. Light weight ceramic proppant was permanently surface modified to a neutral wettability state. This new proppant was evaluated in the laboratory and in the field for compatibility with the fracturing fluid, clean-up properties through the proppant pack and recorded flow back of treatment fluids after a frac-pack operation. Results indicated that the new proppant surfaces not only reduced water saturation but also improved oil mobility. These observations showed the promises of permanently modifying surfaces as next-generation products for improved flow and decreasing the risk of formation damage due to the fracturing fluids left behind after treatment. When this proppant was applied in a frac-pack completion, flow back was efficient with rapid recovery of all pumped fluids. In this case the surface of the proppant reduced the intra-molecular forces between the proppant and the fracturing fluid, eliminating capillary pressure within the frac-pack and leading to a more efficient and quicker fracturing fluid flow back compared to using proppant in its native state. First oil breakthrough was earlier than other wells in the same area.