Sequence Mining and Pattern Analysis in Drilling Reports with Deep Natural Language Processing

Drilling activities in the oil and gas industry have been reported over decades for thousands of wells on a daily basis, yet the analysis of this text at large-scale for information retrieval, sequence mining, and pattern analysis is very challenging. Drilling reports contain interpretations written by drillers from noting measurements in downhole sensors and surface equipment, and can be used for operation optimization and accident mitigation. In this initial work, a methodology is proposed for automatic classification of sentences written in drilling reports into three relevant labels (EVENT, SYMPTOM and ACTION) for hundreds of wells in an actual field. Some of the main challenges in the text corpus were overcome, which include the high frequency of technical symbols, mistyping/abbreviation of technical terms, and the presence of incomplete sentences in the drilling reports. We obtain state-of-the-art classification accuracy within this technical language and illustrate advanced queries enabled by the tool.Comment: 7 pages, 14 figures, technical repor

Geometric Multigrid Methods for Flow Problems in Highly Heterogeneous Porous Media

In this dissertation, we develop geometric multigrid methods for the finite element approximation of flow problems (e:g:, Stokes, Darcy and Brinkman models) in highly heterogeneous porous media. Our method is based on H^(div)-conforming discontinuous Galerkin methods and the Arnold-Falk-Winther (AFW) type smoothers. The main advantage of using H^(div)-conforming elements is that the discrete velocity field will be globally divergence-free for incompressible fluid flows. Besides, the smoothers used are of overlapping domain decomposition Schwarz type and employ a local Helmholtz decomposition. Our flow solvers are the combination of multigrid preconditioners and classical iterative solvers. The proposed preconditioners act on the combined velocity and pressure space and thus does not need a Schur complement approximation. There are two main ingredients of our preconditioner: first, the AFW type smoothers can capture a meaningful basis on local divergence free subspace associated with each overlapping patch; second, the grid operator does not increase the divergence from the coarse divergence free subspace to the fine one as the divergence free spaces are nested. We present the convergence analysis for the Stokes' equations and Brinkman's equations ( with constant permeability field ), as well as extensive numerical experiments. Some of the numerical experiments are given to support the theoretical results. Even though we do not have analysis work for the highly heterogeneous and highly porous media cases, numerical evidence exhibits strong robustness, efficiency and unification of our algorithm

Dynamic Relaxation for Initial Stress Setup and Inelastic Response of Compliant Fault Zones to the Nearby Earthquakes

In this thesis, we first develop a dynamic relaxation technique to obtain the initial stress field that is in static equilibrium for elastoplastic dynamic rupture models using a dynamic solver. Then we examine inelastic response of fault zones to nearby earthquakes. Our dynamic relaxation method mainly relies on a dynamic loading scheme that is applied on the model boundary. The main advantage of such an explicit dynamic relaxation is that the global mass matrix is diagonal. In addition, the global stiffness matrix is not explicitly assembled. There are two main steps in our dynamic relaxation method for obtaining the stress field in the inhomogeneous model: first, choose appropriate boundary nodal force loading for the homogeneous model to obtain the desired stress field; second, apply the same boundary nodal force loading to obtain the stress field for the same size but inhomogeneous model. Through the two steps, we present a viable approach to calculate stress field for inhomogenesous models. We apply the dynamic relaxation technique to study the inelastic response of the Calico and Rodman fault zones to the 1992 Landers earthquake. We develop elastoplastic dynamic rupture models to study the rupture propagation and final slip distribution on the Landers faults. The initial stress field in the elastoplastic model is obtained through the dynamic relaxation method. We present the simulation results of the inelastic response in terms of residual displacement fields on the Earth’s surface, and compare them with the InSAR observations in the East California Shear Zone. In addition, we compare our simulation results with those of elastic models from previous studies and show the advantage of elastoplastic models in term of data matching. The simulation results from our elastoplastic models show better match with the observed data compare to the results from previous elastic models