Horizontal open hole gravel pack (OHGP) completions are increasingly required for the low API gravity oil fields in and near the Campos basin, offshore Brazil. Many successful horizontal gravel packs have been performed in this area, often in spite of increasingly difficult technical constraints on the operation. Critical limiting conditions on successful gravel pack placement include the combination of low fracture gradients, deep to ultra-deep water depths, and extended reach horizontal sections. This paper describes the lessons learned and best practices developed for offshore Brazil horizontal gravels packs under these severe conditions, supported by data from 20 jobs performed to-date. The analysis yields a better understanding of this type of open hole completion and demonstrates how to achieve a successful treatment under critical limiting conditions. Also discussed are several proven completion practices with application for future completion operations in the scenarios presented. Introduction Economic development of deepwater projects demands a minimum number of wells to be drilled and completed in order to effectively drain the reservoir. Heavy oil exploitation makes this approach even more difficult because extended reach wells are needed. Due to the high cost of operating in a deepwater, subsea environment, wellbore intervention must be minimized and completion life sufficient to achieve depletion of the reservoir. Gravel packing of horizontal wellbores in unconsolidated formations has proven to be an effective method to achieve these goals economically in the Campos Basin, offshore Brazil (shown in Figure 1). Stand-alone horizontal completions have common used to complete long, open hole horizontal wells in unconsolidated formations. However, in most applications the stand-alone devices become plugged or cut out with time. The consequences may be unacceptably low well rates or excessive sand production. Therefore, un-gravel packed screens and slotted liners in horizontal completions have been disappointing. Typical reservoirs in Campos Basin giant fields are high permeability turbidite sandstones with low API gravity oil. Generally, these unconsolidated formations are not strongly water driven. Due to the need for high rate injection to maintain reservoir pressure, and since large producers are needed for economic development, it was decided to develop several fields in the Campos Basin with a series of horizontal producers and injectors. Current gravel packing technology offers a great option for a horizontal well completion where sand production presents a problem. The advantages of gravel packing over a stand-alone completion are improved productivity or injectivity and completion longevity. Offshore Horizontal OHGP Best Practices While it is important to effectively prevent sand production, it is equally important to do so in a way that does not hinder productivity. The feasibility and success of gravel packing a long horizontal well depends on drilling techniques, drill-in fluids, wellbore clean-up, open hole stability, completions fluids, completion tools and equipment, sand control techniques, software/simulators, pumping schedules and field personnel experience. Monitoring Return Rate In the early OHGP's performed with floating rigs, the return rate was monitored through the choke/kill manifold with the annular BOP closed. An extremely high circulating pressure was observed during gravel pack pumping.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe economics of the oil and gas production requirements and advanced drilling technologies are often pushing the length of horizontal well to new records. Gravel packing these very long horizontal wells present new challenges to completion operations. The combination of long horizontal sections of unconsolidated formations, low fracture gradients and costly rig time are the other constraints that must be faced in the design and execution of a successful gravel packing completion offshore. Innovative technologies, optimized job design and planning are the keys for the success of packing jobs. This paper addresses several key factors that must be considered carefully in installing a successful gravel pack completion. Pack completion requires that these low fracture gradient wells not be fractured during gravel placement to avoid excess leakoff and premature screenouts. The discussion includes various measures such as optimized screen wash pipe annulus and appropriate using the differential valves, to effectively reduce frictional pressure during Beta wave buildup. Fluid leakoff and leakoff control, in-situ gravel concentration, and their relationship are also discussed. The gravel concentration is dynamically changing through out the treatment based on the flow conditions in the wellbore, especially when the gravel starts to pack around screen. While most of the fluid travels down the screen-casing annulus, portion of the fluid leaks into formation, portion of the fluid diverges into the screen-wash pipe annulus. The results may be an effective in-situ gravel concentration higher than critical concentration, forcing gravel particle deposition to occur too soon and building up a premature bridge.Several job designs and application histories are also presented in the paper to demonstrate the design considerations and valuable lessons learnt. A group of type curves are generated for a quick and easy check during job operation, if any undesired condition is present, the operator can adjust the operation and thus to avoid a job failure. The overall system of fluid dynamics are discussed and treatment guidelines are presented to provide the Completion Engineers the necessary information for designing successful treatments.
In most of its deepwater Campos Basin oilfields, Petrobras' strategy has been to develop the water flooding systems using horizontal gravel packed wells. Both drilling and gravel pack operations are only possible through the presence of a filter cake, formed on the formation face during the drilling process. Nevertheless, that film becomes an impediment to injection and must be removed to obtain good injectivity.Special tools were developed to perform acidizing jobs, in one trip, just after the gravel packing operation. However, there were few alternatives to correct any eventual acidizing lack of performance, besides using coiled tubing and straddle packers, something that usually takes too much time.Recently, a pulse-rotating jet tool system was applied in a well that could not be treated after the gravel pack operation. The treatment, which is simpler and faster than those carried out with straddle packers, was performed in two stages: the first, using just HCl, and the last one, using mud acid.The subsequent formation test performed after the HCl treatment showed a high skin v alue and an unacceptable injectivity index, due the need to keep the reservoir pressure above the bubble point. Even so, the test data in association with reservoir simulation, according with the field geology, showed that there was fluid injection throughout the entire horizontal section. Therefore, it was decided to perform a mud acid treatment, again, using the pulse-rotating jet tool system. This time, a second formation test indicated an excellent injectivity index, confirming the pulse-rotating jet tool system effectiveness and creating perspectives for the application of this technique in future operations. This paper will describe the technique, job details and the results obtained for this particular operation, which may be applied in other similar offshore environments.
The stimulation history in offshore Brazil is undergoing into a deep transformation. The requirements of technology, before focused on sandstone reservoirs demand, are being expanded by the need for techniques to stimulate carbonate reservoirs, specially the pre-salt carbonates. In this scenario, a self-diverting acid system based on a viscoelastic surfactant (VES) technology was introduced for carbonate reservoir stimulation. The Self-Diverting VES (SD-VES) promotes viscosity development when the acid comes in contact with the carbonate formation. The mechanism of viscosity development is simple: In concentrated acid, the system presents low viscosity, which results in friction reduction while pumping; however, when the fluid reacts with the formation and the acid concentration decreases, the micelle spherical structures combine, transforming into rod-like micelles that convert to a 3-D structure, which increases the fluid viscosity. The high viscosity generates a temporary barrier across the high-injectivity zones, diverting the subsequent fluid to treat other reservoir zones. Generally the SD-VES is associated with several placement techniques that aid in achieving good treatment distribution through the entire producer interval. Regardless of the placement technique applied, the SD-VES is generally used as the main acid fluid and is bullheaded into the well. Because of its rheological behavior, the SD-VES is pumped as a single fluid during bullheading, aiming to achieve formation stimulation and good treatment distribution throuth the entire productive interval. Since the SD-VES was introduced in 2009 to treat carbonate reservoirs in offshore Brazil, more than 40 wells have been treated using the system in the various acid placement techniques presented in this paper. Three case histories are presented to better illustrate the different scenarios where the SD-VES was applied.
Proposal Horizontal gravel packs typically employ heavy sand or ceramic gravels, laid down with un-gelled brines in the well-known alpha/beta wave sequence.As operators push the limits of horizontal open hole interval lengths, especially in low fracture gradient formations, it may become technically difficult or economically unfeasible to perform the gravel pack with conventional fluids and gravels. Ultra lightweight gravels allow significant reductions in pumping rate (to avoid fracturing the formation), without risking premature settling and screen-out, therefore, longer wells can be treated.Higher gravel concentrations can also be used, even at low pump rates, resulting in drastic reductions in fluid volumes and treatment time, which is critical in cost-intensive offshore applications.In certain instances, the alpha wave can be eliminated, and the well packed directly in the beta wave mode, from toe to heel. This paper summarizes the development and application of the ultra lightweight media and associated technologies for horizontal well gravel packing.Pioneering case histories will also be reviewed from the initial wells treated. Introduction Horizontal gravel packs have become the completion choice for many operators, especially in permeable and unconsolidated formations.When it comes to deep and ultra-deepwater completions, operators have reached the limit as far as horizontal extension is concerned. The ultra lightweight proppant consists of a resin-impregnated and coated cellulosic particle (walnut hull).The density of the coated particle is approximately 1.25 g/cc.Several laboratory tests were performed prior to field tests to simulate the gravel pack pumping operation, and most importantly, in order to confirm that the ultra lightweight gravel achieves its main objective, which is to provide sand control. Laboratory tests demonstrated that the ultra lightweight proppant can successfully achieve sand control and that alpha/beta wave deposition patterns can be obtained at different rates and concentrations. A large-scale wellbore simulator was used to measure and observe the transportation characteristics of ULW 125 and ULW 175 gravels compared to Ottawa sand and lightweight ceramic proppant.Scientific results of the testing were used to help understand ULW slurry flow properties and predict alpha-wave dune height as a function of wellbore and pumping parameters. At the time of writing, the ultra lightweight proppant had been successfully introduced in two offshore wells with horizontal extended reach sections.Based on these results, it is estimated that the ultra light weight proppant can be used in wells with the most stringent conditions for a horizontal gravel pack: ultra deep water depths, low fracturing gradients, low API gravity oils, and greater than 6000 ft horizontal extensions. Laboratory Tests It was decided to determine the effectiveness of the 1.25 g/cc, 20–40 mesh ultra lightweight proppant, (ULW 125), at retaining unconsolidated sand.For comparison purposes, a 2.73 g/cc, 20–40 mesh ceramic proppant (CP 273) was also tested.The measure of effectiveness was defined as the ability to retain unconsolidated sand without substantial plugging of the gravel pack material. Since the mid eighties, the quality of gravel pack sand has been specifiedby API Recommended Practice 58.The most universally recognized quality specification is that of roundness and sphericity.To look at RP58 in perspective, it was written when the oilfield was using river sand deposits of very poor quality for fracturing and sand control.These low quality sands would generate a substantial amount of silica fines during transportation as well as during pumping downhole.Sorting these sands to a more round and spherical specification would help reduce the amount of fines generated and ultimately pumped downhole. Also, the filtration and plugging characteristics of the round sand grains were well studied and understood by those persons skilled in the art of drilling, completing and stimulating wells.
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