An integrated fully compositional model describing the reservoir, wellbore and surface facilities was implemented and used to allocate the oil and gas production of 72 wells from six different fields. The model was used to simulate all the operational changes occurred in the twenty-year operating life-cycle of the fields, sharing common production and separation facilities. Introduction Sometimes the development and operation of oil and gas fields follows the urgencies of a production policy. In such cases, both the development and operation may be somehow chaotic, not allowing for a proper well testing and well data acquisition; without this information the analysis of a well becomes difficult, and the prediction of future works to improve or maintain its production is not reliable. In such fields, the existing surface facilities are the rigorously needed to transport the production to the selling points. A single stage of separation near the fields is often used to separate the mixture of gas and liquid, so that no production control is observed for each well. Then, the oil and gas streams are mixed with similar streams and finally collected in a common point for processing, measuring and selling. At this common point, the total volume of oil, gas and water is known. Certain methodology has to be used to back allocate the corresponding volume of oil, gas and water to each well in order to estimate its cumulative production and have a correct control of both wells and reservoir hydrocarbon reserves. This operating condition regularly results in non-logical production histories. If these histories are to be used in an integrated study, reservoir simulation or any other study, they have to be revised, since the success of any study relies on the accuracy of the information. For the Muspac and Catedral fields this was the case. These fields were developed and operated without any reliable well production allocation control, so the production histories of these wells were not suitable for its use in the history matching of the simulation models. A new or revised production history had to be used for each field. In order to solve for this problem, an integrated compositional surface-subsurface model with the capability of reproducing the historic changes of a complete production system was conceived and implemented. This model generated the new production histories for both fields.

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The main objective of this paper is to present acertification process to achieve the reliability of well log data for any user, independently where or when the log was ran. For example, the analogical log data (old data) is digitally recaptured and processed through quality control criteria's, edited and spliced curve by curve, where all technical steps are documented in the corresponding digital file in order to provide the user the details of how the technical process was used and made. Finally, a digital signature certifies all files. At that moment anyone can use the certified products for interpretations, correlations or petrophysical evaluations. As it is the case in most oil producing companies, two log data generation are present in Mexico: analogical and digital. Analogical process was initiated in 1904, when the first well was drilled, and the digital process began in 1979 through the "Cyber System Unit" used by Schlumberger. Those two generations, analogical and digital log data, demand new technologies and process to equalize the quality of old and modern data in order to use and manage this information in applications and databases. The certification process includes on line log inventory using the log and services codification published by The American Petroleum Institute (API), log quality control routine for "Digital Log Interchange Standard" (DLIS), "Log Information Standard" (LIS) and "Log ASII Standard" (LAS), including: originals, edited and spliced logs. The authenticity and reliability of each file is warranted by a digital signature, it specifies who made the process and who accepted the final product. The certification process was designed to equalize the quality of analogical and digital log generations, to establish the log reliability for any user and, finally to improve the data management. All these factors impact positively log data base preparation for project execution. Past, present and future of well log data On September 5th, 19271, when Schlumberger brothers run the first electric log in a well in France's Pechelbronn field, began the well logging era to nowadays. Afterwards, many kinds of logs and logging technologies have been developed in order to obtain more information and details from the subsurface. Now, two well differenced log data generation are present: analogical and digital. Many efforts have been done in order to equalize the analogical generation into digital data in terms of formats and quality controls. To support this goal, the main scope of this initiative is to provide all logs: open and cased hole, to any user in terms of integrity and reliability allowing the users to use those directly, including master log inventory; original, edited and spliced well log data. All products in this process have to be validated for the processor and certified for the data owner. As this process is applied over preexistent log data, it has to be applied over new log data (new acquisition) in order to guarantee similar standards for both log data generations. Finally all logs from a present or future well are conceived as an integrated product where the analyst can use the master inventory and download the certified data that he/she requires for his / her technical activities. Figure 1 shows the general certification process and its products. Well log data Certification Process The general certification process includes open and cased well logs; however, for this paper only open hole logs will be considered. The General Certification Process (Figure 1), includes the following sub process:Certification Process for analogical log data. (Figure 2)Certification Process for digitally captured log data: LAS format (Figure 3) Certification Process for digital origin data: LIS / DLIS format (Figure 4)

An operation model for mature field not only should be used during a world oil price crisis, but also it should be incorporated as a best practice during the life of the oil field, consequently, in mature field projects it is always possible both to improve its profitability indicators and to increase its hydrocarbons production. One of the most important challenges is to incorporate these actions as a mature field management culture by supporting existing facilities operations and field elements using best practices focused on processes, human resource skills and technological elements. Operators have a great opportunity concentrated in these key aspects to optimize results by reduction and optimization of costs and improvement of operations. The objective of this paper is to provide a practical guide to be considered during the field operation and management of mature asset, addressing actions to maximize the operation efficiency, maximize the hydrocarbon recovery factor and to optimize costs and resources. It describes an integrated operations process for low profitability projects/fields, like mature fields and marginal fields, summarizing best practices to identify opportunities in existing operations. The paper also describes how to find opportunities by clear understanding the relationship among key processes such as:Reservoir Management and Surveillance,Water Management, Waterflooding and EOR,Drilling, Completion, and Production Engineering,Artificial Lift Management,Efficiency and Cost Control.Suppliers and service company's management These best practices addressing organized processes, human resource skills and technology elements are described clearly and they are presented as tools for easy implementation. Case studies in Mexico and Argentina are shown, along with management models for implementing, surveilling and maintaining mature fields which resulted in lower operation costs and a sustained oil production increase.

There are many mature fields in Latin America. Beyond the definition of maturity applied, the common factor to all of them is that surface facilities and field operation have been running for many years. This is one advantage to generate profits.However, operations are governed by old practices for defining profitability of wells and in some cases do are not specifically developed or evaluated for these wells, therefore, underestimate the economic return generated.