COMPLEX CRITERIA OF ASSESSING LITHOLOGICAL OBJECTS FOR DRILLING PROSPECTING WELLS AT THE NORTHERN EDGE OF THE DNIEPER-DONETS DEPRESSION

Abstract

The article tells about the process of selecting basic criteria for assessing the expediency of drilling to prospect the lithological objects within the Northern Edge of Dnieper-Donets Depression. The work proposes detailed description of the types of analysis required in order to decide whether it is reasonable to drill a prospecting well to target the lithological object. It offers to regard the examples of the lithological objects with and without the presence of the structural factor in Moscovian and Bashkirian deposits. A real example of successful identification of the lithological object within Moscovian horizons M-6 and M-7 has been demonstrated. The conclusions of the performed analyses have been confirmed by the actual drilling results. Specific analytical approaches have been demonstrated upon the condition of seismic wave field anomaly presence confirmed by various seismic attributes (pre-stack and post-stack). The main tool for working with non-structural bodies is detailed quantitative interpretation of the identified objects. Based on the described material this article recommends to perform, at least, the AVO study and pre-stack inversion. If all quantitative attributes demonstrate the same positive result, such object should be recommended for prospecting drilling. In case, different methods provide different results, it indicates high probability of water saturation in the horizons within the positive lithological conditions. Three main alternative criteria have been identified to serve the basis for lithological objects assessment and making the decision on expediency of the prospecting drilling. Within the Northern edge of the Dnieper-Donets Depression, those three criteria are: 1) the shape of seismic anomaly – the more mosaic it is, the higher probability that it has been shaped at the account of residual/weak gas saturation or it is due to specifics of the processing/field acquisition; 2) the area of seismic anomaly (typically, seismic anomalies proven by drilling within the Northern Edge of DDD have area of 1 km 2 and more); 3) correlation of seismic anomaly with earlier drilled wells (and their drilling results in certain horizons) and negative mini-depression type structural anomalies.