A Strategic Gas Field Development Case in Sandstones Using Seismic Amplitudes and Dynamic Characterization
Authors: Arevalo-Villagran J.A. , Cinco-Ley H. , Gutierrez-Acosta T. , Martinez-Romero N. , Garcia-Hernandez F. , Wattenbarger R.A. 
Published: March 2010

Abstract
The objective of this paper is to present a process for improving the planning of gas field development. We discuss how static and dynamic characterization can be combined to help optimize gas field development. The main concepts, methodologies, and results are shown for an actual Mexican gas field. Static characterization centred on a series of seismic amplitude maps constructed from 3D seismic interpretation. Dynamic data included production data and initial pressure gradients which were useful in delineating individual reservoirs and establishing hydraulic communications between certain reservoirs. The seismic amplitude maps, modified by considering the dynamic data, improved the evaluation of reservoir quality, the estimation of drainage areas, original gas-in-place, and proved reserves. A strategy for the optimal field development was designed by using this combination of seismic amplitude maps modified with information from logs, cores, production, and pressure data.

Introduction
The subject gas field is located in the central area of the Veracruz basin southeast of Veracruz, Mexico. The field was discovered in 1921 with Well 1, which was drilled by a foreign company. The field is formed by many lenticular sandstones containing gas at abnormal pressures.
The first producer well (Well 3) was completed in 1962 in Tertiary sandstones. The field has had a total of 24 wells drilled, in addition to Well 1. Fourteen wells are now gas producers (Wells 3, 4, 5, 6, 201, 402, 403, 404, 405, 406, 412, 415, 420, and 436), nine wells have watered out (Wells 10, 12, 13, 15, 101, 407, 414, 428, and Ma-1), and one well was lost because of mechanical failure (Well 102).
Currently, the gas field is comprised of three main producing sandstones: the sandstones at the base of the Lower Pliocene (body "E" located at 1,600 - 1,680 m or 5,249–5,512 feet of depth) which began development in November 1969 with Well 5; the sandstones of the Upper Miocene (body "G" located at 2,050 - 2,250 m or 6,726 - 7,382 feet of depth) which began development in August 1966 with Wells 3, 4, and 6; and, the sandstones of the Late Medium Miocene (body "M" located at 2,500 - 2,700 m or 8,202 - 8,858 feet of depth) which began development in August 1988 with Well 201.
Table 1 shows the well names, the reservoir, and fluid data for each producing sandstone.
In 1999, a series of 3D seismic surveys were performed covering an area of 240 km2 (59,305 acres). The interpretation of the 3D seismic surveys allowed the construction of several seismic amplitude maps. These maps were used for detecting significant volumes of gas related to high seismic amplitude areas, while establishing geological models and delimiting stratigraphic features.
The seismic amplitude maps were calibrated with reservoir and fluid properties as well as production data obtained through productive wells from different sandstones. Using these modified maps then led to an improved development plan for the field.
The fundamental objective of this work is to present the methodology and results of the teamwork aspect of this integrated reservoir management study.