Paleoenvironmental Conditions during the Paleocene–Eocene Transition Imprinted within the Glauconitic Giral Member of the Barmer Basin, India

The roughly 6 m thick limestone–green shale alternation within the lignite-bearing Giral Member of the Barmer Basin corresponds to a marine flooding event immediately after the Paleocene–Eocene transition. A detailed characterization of the glauconite using Electron Probe Micro Analyzer (EPMA), X-Ray Diffraction (XRD), Mössbauer and Field Emission Gun-Scanning Electron Microscope (FEG-SEM) reveals its origin in the backdrop of prevailing warm climatic conditions. The glauconite pellets vary from fine silt-sized to coarse sand-sized pellets, often reaching ~60% of the rock by volume. Mineralogical investigation reveals a ‘nascent’ to ‘slightly evolved’ character of the marginal marine-originated glauconite showing considerable interstratification. The chemical composition of the glauconite is unusual with a high Al2O3 (>10 wt%) and moderately high Fe2O3(total) contents (>15 wt%). While the K2O content of these glauconites is low, the interlayer sites are atypically rich in Na2O, frequently occupying ~33% of the total interlayer sites. The Mössbauer spectrum indicates 10% of the total iron is in ferrous form. High tetrahedral Al3+ of these glauconites suggests a high-alumina substrate that transformed to glauconite by octahedral Al-for-Fe substitution followed by the addition of K into the interlayer structure. The unusually high Na2O suggests the possibility of a soda-rich pore water formed by the dissolution of alkaline volcanic minerals. The Giral glauconite formation could have been a part of the major contributors in the Fe-sequestration cycle in the Early Eocene shelves. Warm climate during the Early Eocene time favored the glauconitization because of the enhanced supply of Fe, Al, and Si and proliferation of an oxygen-depleted depositional environment.

An Innovative Approach of Using Engineering Modelling to Improve Drilling Dynamics in Western Rajasthan, India

Raageshwari Deep Gas (RDG) field is a major gas field in the Barmer Basin of Rajasthan, India which comprises of a tight gas-condensate reservoir within the underlying thick Volcanic Complex. The Volcanic Complex comprises two major units – upper Prithvi Member (Basalt) and lower Agni Member (Felsics interbedded with older basalt). The production zone is drilled in 6" and has historically seen high level of shock & vibrations (S&V) and stick-slip (S&S) leading to multiple downhole tool failures and poor rate of penetration (ROP). Individual changes in Bit and bottom hole drilling assembly (BHA) design were not able to give satisfactory results and hence an integrated approach in terms of in-depth formation analysis, downhole vibration monitoring, correct predictive modelling, bit and BHA design was required. A proprietary formation analysis software was used to map the entire RDG field to understand the variation in terms of formation compactness, abrasiveness and impact (Figure 1,2,3 & 4). The resulting comprehensive field map thus enabled us to accurately identify wells that would be drilling through more of problematic Felsics and where higher S&V and S&S should be expected. To better understand the vibrations at the point of creation, i.e., bit, a downhole vibration recording tool was used to record vibration & stick-slip data at a frequency of 1024Hz. This tool picked up indication of a unique type of vibration occurring downhole known as High Frequency Torsional Oscillation (HFTO), that was quite detrimental to the health of bit and downhole tools. A proprietary predictive modelling software was used to optimize the bit-BHA combination to give least amount of S&V and S&S. Data from the downhole vibration recording tool, formation mapping software and offset bit designs was used to design a new bit with ridged diamond element cutters and conical diamond element cutters to drill through the highly compressive and hard basalt. The predictive modelling software identified a motorized Rotary steerable assembly (RSS) to give the best drilling dynamics with the newly designed bit. The software predicted much lower S&V and S&S with higher downhole RPM which was possible with the help of motorized RSS. Implementing the above recommendations from the various teams involved in the project, drilling dynamics was vastly improved and ROP improvement of about 45% was seen in the field. This combination was also able to drill the longest section of Felsics (826m) with unconfined compressive strengths as high as 50,000 psi in a single run with excellent dull condition of 0-1-CT-TD This paper will discuss in detail the engineering analyses done for improving drilling dynamics in field along with how HFTO was identified in field and what steps were taken to mitigate it.