Because many oilfield workers see matrix treatments of wells as a low-tech operation, they often fail to pay attention to candidate selection and treatment design. This lack of attention may have led to the relatively low success rate of these treatments. A 1997 survey in a major oil company indicated that one out of every three to four jobs fails to produce more oil or gas after the treatment. This failure represents a loss to the company of over $10 million (U. S.), plus a missed extra production capacity of nearly 40,000 BOPD. The probable main cause for this poor performance is the lack of a structured approach to the following:selecting the right candidate wells and the appropriate treatmentdefining and implementing a structured treatment design procedure To improve the situation, a task force investigated the problem and mapped out a total process, which consists of the following steps: A candidate well is selected by comparing its actual performance against its theoretical potential. Then, the source of poor performance is identified, if applicable. Based on this information, the treatment type can be identified and designed, ultimately resulting in an operational stimulation program. The task force concluded that individual pieces of design software and some design rules existed for many elements, but they lacked an integrated overall approach. The team decided to create a software package by integrating "fuzzy" rules with appropriate mathematical models to guide field engineers through the individual design steps in a consistent, structured manner. This paper describes various elements of the integrated software package that was designed to meet these needs. Background Soon after the first wells were drilled, people started to look for methods to improve the production of new and existing wells. In 1895, a well in Ohio, U.S.A. was successfully treated with hydrochloric acid (HCl) for the first time. However, until the early 1930's, when arsenic inhibitors emerged, the lack of good corrosion inhibitors prevented acid from being widely used to stimulate wells. The use of "mud acid" was then introduced for sandstone wells. In subsequent years, additional techniques, materials, and equipment were further developed, leading to widespread stimulation activity. Today, several thousand treatments are completed worldwide each year, with a total expenditure of many millions of U.S. dollars. Most of this money is spent on matrix-acidizing treatments. Stimulation is popular primarily because it is probably the most economical way to generate extra production capacity. For instance, a Dutch oil and gas company carried out a stimulation campaign in the prolific Groningen gas field, although the well rates were already approximately 1. 5 million m3/d. A total of 16 wells were treated with acid, resulting in an approximate net increase of 3.6 million m3 /d of gas (at 100 bar FTHP) at a total cost of $600,000 (U.S.). Had the company chosen to obtain such potential by drilling new (infill) wells, they would have spent approximately $7.5 million.

Horizontal drilling and multistage hydraulic fracturing have been credited for much of the success achieved in ultralow permeability shale reservoirs, making it possible to produce natural gas, natural gas liquids, and crude oil at economic rates. Although thousands of wells have been drilled and completed using these techniques, there are relatively few design tools and processes available within the industry designed specifically for these applications. In the past, much of the optimization process has been the result of trial and error techniques that can be both costly and time consuming. This paper examines a step-out development project where new processes and tools were used to accelerate the de-risking of the asset area by identifying the best quality reservoir targets and significantly improving production and economics by implementing a completion optimization process. This reservoir centric process uses earth modeling, complex fracture modeling, and reservoir simulation tools developed specifically for shale type formations. It also focuses on designing the wellbores to best accommodate the staged stimulation treatments that can help maximize the stimulated volume and the connected fracture area within this volume. When optimized, this process can help maximize the estimated ultimate recovery (EUR) while sustaining economically viable production rates. A detailed example is presented illustrating how these tools were successfully applied within a new development to accelerate reservoir understanding, help improve well performance consistency through more effective well placement, and significantly increase well performance through applied engineering processes, completion designs, and effective stimulation treatments. The success of the project is discussed to illustrate both the initial and sequential performance improvements as new processes and designs were implemented. Total well cost comparisons are also included to verify the economic benefit achieved within this asset.

Despite significant improvements in completion technology, water production problems associated with encroachment, channeling, and coning still prevail in' many wells. In this paper, different types of water-producing wells are classified corresponding to their onset mechanisms. Various applications of polymers and cements in minimizing water-oil ratio are reviewed. Methods and limitations of current water control processes are evaluated. A general procedure for designing water-control treatments is presented. This paper also addresses difficulties existing in design and performance of water-control treatments. These include (1) lack of an extensive production history and knowledge of prior stimulation of wells requiring treatment, (2) lack of a systematic approach in treatment design, and (3) improper recovery techniques when returning the well to production. Results of wells treated in various fields are evaluated with respect to methods and chemicals used. Information presented in this paper will provide the completion engineer a broad knowledge of water-control treatment design parameters and chemical applications currently available within the industry.

The use of horizontal drilling and hydraulic fracturing has been credited for much of the success achieved in ultra-low permeability shale reservoirs, making it economically possible to produce natural gas, natural gas liquids, and crude oil. Although thousands of wells have been drilled and completed using these technologies, there are relatively few modeling tools available to the industry designed specifically for these applications, leaving much of the optimization process to trial- and-error techniques that are costly and time-consuming. A focused effort to develop useful software tools for industry professionals to better design and more reliably predict well performance has resulted in a new generation of hydraulic fracture and reservoir simulation tools built specifically for these complex well geometries and difficult reservoir conditions. These tools have also been designed to provide information that can enable completion engineers to make informed decisions to help ensure the desired results are achieved and well performance maximized. The workflow is focused on designing stimulation treatments that maximize the stimulated volume of the reservoir around the wellbore and also maximizes the connected fracture area within this volume. This combination can result in increased production rates while also increasing the possible ultimate recovery that can be achieved from a given wellbore, thus having a significant impact on the economic success of a well and an entire asset. This paper provides details on these new tools and workflows, as well as the results of early trials that have yielded impressive results, even when applied in an established shale field within the US.

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