With Gulf of Mexico (GOM) hydrocarbon discoveries reaching record depths and very high bottomhole pressures, the need for proven, weighted fracturing stimulation fluids has become urgent. As previous studies have shown, frac packs have a significant impact in maintaining well productivity in the later production life stages of unconsolidated reservoirs. Thus, sustaining the ability to pump frac packs in these challenging environments is a priority.With conventional frac pack fluids, these greater depths and higher bottomhole pressures often would result in the need for surface treating pressures that exceed the limits of current surface equipment and tubulars. Surface treating pressure can be calculated using the equation: P s = BHTP + P fric -P hyd …………………….. (1) P s = surface pressure BHTP = bottomhole treating pressure P frict = friction pressure P hyd = hydrostatic pressureThe equation shows that an increase in hydrostatic pressure results in a reduction in surface pressure. This is true as long as any corresponding increases in BHTP and friction pressure remain below the hydrostatic increase. If substantial reductions in surface pressure can be achieved, then frac pack treatments remain a safe and viable option in deepwater and ultradeepwater environments.As of October 2007, sixteen total jobs have been pumped with a weighted frac pack fluid. Of these jobs, eleven treatments have been pumped by Chevron in the deepwater GOM. This paper presents data from these treatments where substantial reductions in surface treating pressures were observed. Also shown is the accuracy to which surface treating pressures with the weighted frac-pack fluid can be predicted.

Industry experience has shown that frac pack completions can provide effective production stimulation and reliable sand control for unconsolidated sand reservoirs. One of the more rewarding areas of opportunity is in the completion of longer and more complex intervals that can be stimulated with a single frac pack treatment. Here, the cost saving of a single completion versus the cost of two or the recovery of reserves from pay zone sand added to the completion interval can add significantly to the cash value of the well. This paper discusses an innovative screen that has a concentric shroud that can treat two separate and distinct sand lobes during a single frac-pack operation. Two cases histories illustrate the use of an innovative assembly that uses the new screen to enhance the stimulation and sand control results of frac pack completions on unconsolidated sand reservoirs with complex lithology and permeability contrast. The capabilities of this technology have brought a long-sought-after solution to fruition. Introduction Although conventional screens have been very successful in controlling sand production in most situations,1,2 not every well configuration lends itself to traditional screens. For example, in completions where there is a risk of screening-out in the upper part of the completion before the lower part of the completion, a screen-out with conventional screens can prevent the gravel slurry from reaching the lower part of the completion. Questionable applications include:frac packs where potential annular restriction or bridging may compromise sand control or uniform stimulation of the pay intervalfrac packs in intervals where there are distinct layers with different lithologyfrac packs in intervals where there are significant variations in permeability and porosityfrac packs in long intervals where there is concern that a complete annular pack would be achievedfrac packs in highly deviated intervals where multiple fracture initiation may jeopardize complete annular packing. Because of the more complex completions now attempted, the incidence of failures experienced in scenarios such as those listed above have increased. To provide a solution, a new type of sand-control screen assembly that consists of an outer perforated shroud placed over a metal-mesh sand screen has recently been developed. With this assembly, the annular space between the outer shroud and screen forms a secondary slurry flow path to enable bypassing a blockage in the outer annulus between the shroud and the casing. The perforations in the shroud are designed to balance slurry flow control during the treatment and low inflow restriction during production.

In the 1980s, economic conditions in the oilfield were demanding improvements in economic and completion efficiency, and all phases of the industry were requiring that strategies to improve cost be revisited. Sand-control completion methodologies were no exception; they were no longer capable of meeting the economic and completion-efficiency required to complete the long stacked intervals being attempted. To address this problem, a single-trip multiple-zone gravel-pack system was developed. The concept was successful for the targeted formations, but as with all new technologies, certain shortcomings concerning rathole intervals, complexity of the systems, and longer, more deviated wellbores prevented its use in all types of reservoir scenarios.An improved version that was introduced in the early 1990's attempted to address these shortcomings. This system was successfully deployed and is still being run in the Far East today. However, limitations that were still experienced with the single-trip multiple-zone systems have prevented their wide spread adoption, causing them to remain a niche completion technique predominately used in the Far East and Italy.Industrial drivers for deepwater development have again caused operating companies to revisit the viability of multiplezone systems. Once considered too complex and risky for offshore operations; the development of the ultra deepwater lowertertiary play in the Gulf-of-Mexico has provided the impetus for renewed interest in multi-zone concepts. This interest has been driving the development of the latest generation of the cased-hole multiple-zone system as well as an openhole multiplezone frac-pack-compatible completion system. The intent of this paper is to chronicle the development of cased-hole single-trip multiple-zone completion systems with a focus on the latest generation of these systemsthe systems developed for deepwater applications. The paper will also discuss why previous systems have not proliferated globally to become an accepted mainstream sand-face completion technique.The improved functionality of the newest system will be described and compared to the previous generation of systems. The integration testing to qualify the new multiple zone system is included in the discussions. Several installations have been planned, and the case histories will be included if available by paper time.

No abstract

When the first frac pack was performed in the Gulf of Mexico (GOM) over a decade ago, very little was known about the effects this form of sand control would have on the intended formation. Even less was known about how to optimize the treatment to get the most benefit for the formation. Since that time, the sand control community has learned a great deal about the effects and benefits of frac packing various unconsolidated formations throughout the world. However, most of the knowledge and design criteria have been housed within the minds of individuals and cannot be looked at as a whole to find trends and fine tune the design methods currently being used. Another complicating factor is the number of frac models being used within the industry with varying degrees of complexity. Therefore, even though thousands of frac packs have been performed globally, frac-pack redesign methods are still subjective and differ from individual to individual and model to model. The recent creation of a database that houses selected formation evaluation test (FET) and frac data, along with model-specific parameters, allows full-scale analysis of a large number of jobs pumped in the Gulf of Mexico. With a consistent analysis procedure in place, the database, populated with numerous treatments by engineers working throughout the GOM, can be analyzed objectively. The data contained in this database include rock mechanics, net pressures, pumping trend data, tip screenout (TSO) times, etc. This paper explains the methodology and discusses the results of the database analysis, using case studies to determine the best method for analysis of the jobs. Crossplots show the correlation between TSO prediction and actual events and suggests recommendations for more successful future design work. This paper is meant to give up-to-date guidelines to help design better frac packs. Introduction Within the sand control community, the ability of an engineer to redesign a frac pack from data generated during the minifrac can sometimes be considered more art than science. Often the engineer whose job it is to formulate the frac pack treatment will use several different methods to arrive at a solution deemed most correct. Many hours are dedicated to determining the proper design for a frac-pack treatment. While often the results cannot be argued, it is unwise and possibly a waste of time to reinvent the wheel for every job. Rather, it should be the goal of the sand control and frac-pack communities to develop a design method that can determine the most important parameters necessary to complete the job. This method would be easily repeatable and could be used throughout the GOM and possibly in other high-permeability, unconsolidated regions of the world. The purpose of this paper is to solve the problem previously described. The goal of the project was to accurately predict the TSO event such that the fracture geometry could be better understood. In fracture theory, the TSO[1] is the point at which there is no longer any propagation of the fracture length. Most fracture models treat this as the time at which the first grain of sand is exposed to the tip of the fracture, ceasing any further growth and allowing net pressure to accumulate and build width throughout the length of the fracture. The creation of a standard reliable method for predicting the onset of the TSO event would enable engineers involved in designing frac-pack operations to become more aligned in their procedures, as well as provide more accurate results. Knowing which "knobs" within the fracture model should be manipulated in order to get the most accurate results would be invaluable. This would allow for much quicker analysis of the data accumulated from the minifrac thereby saving expensive rig time. In addition, should multiple engineers be analyzing the data, a single reliable method would allow a much more concrete determination of any issues because everyone should see very similar results. There have been many efforts to do this in the past.[2] This paper presents the methodology behind developing a database system to track frac-pack treatment data, what data was deemed necessary to a reliable model, and the procedure for procuring that information from various fracture treatments. Then, case studies are presented that prove that the model, populated following the recommended procedure, accurately predicts the TSO event in various situations.