--> Effective Reservoir Identification and Controlling Factor Analysis for Mixed Sediments in Saline Lacustrine Basin, Shizigou Area, Qiadam Basin, China

AAPG ACE 2018

Datapages, Inc.Print this page

Effective Reservoir Identification and Controlling Factor Analysis for Mixed Sediments in Saline Lacustrine Basin, Shizigou Area, Qiadam Basin, China

Abstract

The Lower Ganchaigou formation of Eocene in Shizigou area is characterized as mixed sediments in saline lacustrine basin. It contains various contents of complex minerals, and the effective reservoirs are difficult to identify from conventional logs due to the complex pore structures. It is well known that the pore space connected to fractures, solution enhanced bedding planes, and vugs greatly enhance the fluid flow. Characterizing these different pore spaces in carbonates has been a great challenge for petrophysicists and reservoir engineers for many years. In this study, we proposed a new workflow which merges texture analysis, image porosity analysis, and fracture extraction to describe and quantify the full porosity distribution from electrical borehole images. And incorporating the core analysis data as well as production data, the best reservoirs were identified, and the main controlling factors were concluded.

Based on spectroscopy data and XRD data, the different mineral contents can firstly be quantified, and hence porosity can be derived by using the optimized method. Then the textures of the formation can be classified into five different types from resistivity image data, named thinly laminated, interbedded, sedi-massive, cracked and deformed. Conductive fractures are evaluated by quantitative parameters including fracture density, aperture and porosity. What’s more, conductive heterogeneities (fractures and vugs) are delineated on the image using thresholds on contrast and value, and conductive inclusion surface proportion and conductive inclusion size can be derived. And by comparing the minerals, porosity, textures, fractures, conductive heterogeneities with production data, the controlling factors of the productive reservoirs can be identified, and the criteria of effective reservoir can be established.

40 wells have been processed and analyzed by this method, and it was found that the high production zones are prone to have high dolomite content with cracked texture, and fractures or solved vugs are quite developed. By integrating with the structure analysis, faults developed close to these pay zones are thought to have great impact on fractures and vugs.

Conventional logs have low vertical resolution and often fail to predict accurately the production potential of these complex reservoirs. Accuracy has been greatly improved since the introduction of microelectrical borehole image logging and subsequent interpretation workflows.