Use of Modern Reservoir Characterization in Mature Fields To Unravel Hidden Reserves
Authors: Carpenter Chris 
Published: February 2017

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 177195, “Application of Modern Reservoir Characterization in Mature Fields To Unravel Hidden Reserves,” by M. Rodriguez, F. Abad, L. Rodriguez, and J. Gaibor, Halliburton, and M. Moran and A. Verdezoto, Petroamazonas, prepared for the 2015 SPE Latin American and Caribbean Petroleum Engineering Conference, Quito, Ecuador, 18–20 November. The paper has not been peer reviewed.

This paper discusses the successful, fully integrated, 3D Earth modeling (EM) and dynamic reservoir simulation of the Hollin Formation in the Lago Agrio Field within an operator’s first producer field in Ecuador. Early feedback of reservoir heterogeneity helped in understanding key reservoir issues and developing the methods undertaken to solve various problems. The implementation of cutting-edge reservoir-modeling techniques contributed to improving production rates and enhancing recovery.

Available Data

Lago Agrio has features of a mature field: more than 43 years of production history, 75% of extracted official re-serves P1 and P2 (quantified by the operating company), and a declination from plateau production of 31%, along with a steady decline of the field. New drilling and the workover of existing wells during the reservoir productive life have not been able to increase production. Abundant data exist from a number of wells in the Lago Agrio Field, such as from conventional-log-suite core analysis, pressure/volume/temperature fluid tests, pressure buildup, and a broad production history.

Discussion and Results

Sedimentological Model. Several authors define three depositional environments for the sediments of the Hollin Formation: fluvial, tidal-dominated, and shallow marine. How-ever, the thickness and lithofacies of these intervals vary from field to field. A sedimentological study was performed with core data, core descriptions, bore-hole well logs, and general knowledge of the Oriente Basin.

Petrophysical-Properties Modeling. Diagenetic Analysis. X-ray diffraction and scanning-electron- microscope (SEM) data allow analysis of the mineralogical features in the fluvial, tidal, and marine intervals of the Hollin formation. In the fluvial/tidal Hollin interval, it is observed that quartz is the predominant mineral, followed by clay minerals; calcite and illite minerals were observed toward the top. The most common clay mineral is vermicular kaolinite. Siliceous cement was observed in patches. Toward the top, evidence of calcareous cement is shown. Meanwhile, in the marine Hollin interval, the predominance of glauconite and a significant percentage of ankerite are observed.

The existing differential diagenesis between the fluvial/tidal and marine units markedly affects the textural characteristics of the rock and the relationship of flow/storage capacity; therefore, it becomes extremely important to model permeability and rock types (RTs) separately for these units.

Porosity Correction. Porosity measurements on core plugs were conducted by various methods and at various pressure confinements. This generated the need to standardize the information before it was used to compare with logs and create models of RTs. In the first in-stance, net confinement pressures were calculated for each reservoir. Then, with the help of the rock- compressibility analysis from a neighboring analog field, the pore volumes were normalized, obtaining porosity changes per each confining-pressure increase.

Once core porosity was corrected, the log-core calibration was achieved. The best porosity estimation is given by density neutron because it evidences clay content and calcareous cement correctly.