Study on Wellbore Stability of Shallow Sediments in Deepwater Drilling
Method: In this paper, the shallow formation around the borehole is divided into plastic zone and elastic zone considering it under nonuniform in-situ stress. The collapse pressure formula of shallow formation is derived by taking the shrinkage rate of the borehole as the instability criterion. The fracturing pressure calculation model of shallow sediment under non-uniform in-situ stress is derived by combining the theory of excess pore pressure and hydraulic fracturing.
Experimental Evaluation of Separation Methods for a Riser Dilution Approach to Dual Density Drilling
A dual gradient, deepwater drilling system based on dilution of riser mud requires economically separating the riser mud into a low density dilution fluid and a higher density drilling fluid. This study investigated the practicality of accomplishing this separation using hydrocyclones and centrifuges and examined the possible benefits and efficiency of each. The separation experiments were conducted using a laboratory centrifuge and 2 inch hydrocyclones. The laboratory centrifuge was able to separate the riser mud into near ideal densities for dilution and drilling fluid. However, the dense slurry retained in the centrifuge had lower emulsion stability than the feed stream. The hydrocyclones achieved much less contrast in density between the low and high density discharges, but consistently resulted in a beneficial increase in the stability of the mud emulsion in all of the flow streams and had more desirable rheological properties. A qualitative comparison indicates that the hydrocyclone separation system may offer a feasible and desirable alternative to centrifuge separation system.Copyright © 2009 by ASME
SubSea MudLift Drilling Joint Industry Project: Delivering Dual Gradient Drilling Technology to Industry
In early 1996, a consortium of deepwater drilling contractors,operators, service companies and a manufacturer gathered to discuss potential approaches to "riserless drilling", also known as "dual gradient drilling". This technology overcomes a significant deepwater drilling challenge: eliminating some of the casing strings necessitated by the relatively high pore pressures and low formation strengths found in areas like the deepwater Gulf of Mexico. That initial workshop led to what has become one of the largest and most significant joint industry projects (JIPs) in the history of our industry: the SubSea MudLift Drilling JIP. The JIP's overarching goal became to provide a total solution for dual gradient drilling, that is, both hardware and the methodology to safely and efficiently use that hardware. Five years and nearly 50 million dollars later, this JIP has succeeded in that goal. This paper, the first in a series of three on SubSea MudLift Drilling (SMD), will present highlights of the history of the project, its organization and its management (see also SPE 71358 and SPE 71359). The information presented here demonstrates the level of effort necessary to produce a ready-for-application technology, and will assist anyone planning a major JIP to deliver a complex new technology. Additionally, it will discuss the development of the SMD equipment, the preparation of SMD-specific drilling and well control procedures and the complementary relationship between those procedures and the equipment design. This paper will verify the integrity of the process used to develop these procedures, and it will help the reader understand the SMD system and techniques developed by the SMD JIP.