Innovative Fluid Identification Method in Tight Oil Reservoir By Combining Nuclear Magnetic Resonance Data With Array Dielectric Measurements and Spectroscopy Data

Abstract

In China, more and more unconventional reservoirs have been targeted as active exploration area, such as Chang7 tight oil reservoir in Ordos basin, Sha3 tight oil reservoir in Bohai Bay. In these unconventional reservoirs, the porosity is usually lower than 10%, and pore structure is complex, sometimes formation water salinity may vary a lot. As a result, resistivity loses the sensitivity to fluid types. In this study, an innovative reservoir evaluation and fluid identification method was established by combing nuclear magnetic resonance data with array dielectric contants and spectroscopy data , and the interpretation coincidences rate was improved a lot. The dielectric constant of water is very different from that of oil and other formation components, making dielectric measurements particularly useful for saturation evaluation independent of resistivity. In complex reservoirs, pore structure also plays an important role in the producible fluid types. The combination of dielectric and nuclear magnetic resonance data overcame this difficulty by incorporating resistivity-independent saturation with reservoir heterogeneity information. So, core data, spectroscopy, and nuclear magnetic resonance data were used to analyze the properties related to reservoir heterogeneity, such as mineral content, pore-size distribution, irreducible water-filled porosity, and free fluid porosity. By comparing these properties with the water-filled porosity from array dielectric measurements, the producible fluid types can be determined. The method has been used in more than 30 wells in different oilfields across China, and the testing results have demonstrated the effectiveness of the proposed method. Producible fluid identification is improved when the oil saturation from dielectric measurements is integrated with reservoir heterogeneity information from other measurements. Although the depth of investigation of dielectric measurements is limited to several inches, invasion is typically shallow in low porosity and low permeability reservoirs, and so oil saturation derived from dielectric measurements approximates the saturation of the undisturbed formation. This method has also been applied well accepted by different operators across china and achieved big success.

AAPG Datapages/Search and Discovery Article #90332 © 2018 AAPG International Conference and Exhibition, Cape Town, South Africa, November 4-11, 2018