Drilling Hazard Mitigation Method
Authors: Antipova Ksenia , Kulakova Olga 
Published: October 2015

An analysis carried out using the Orenburg area and Karachaganak field examples demonstrates that the most intense absorptions, oil and gas blowouts, and caving hazardous areas are associated with unconsolidated reservoir development intervals.

The purpose of this work is to develop a method for predicting abnormal reservoir interlayers in order to prevent potential problems through the use of optimal drilling conditions.

Present-day requirements to the accuracy of determining highly permeable interlayer occurrence intervals necessitate the development of a catagenetic occurrence model and carrying out a detailed analysis of core material.

Petrographic and mineralogical investigation methods; bench scale porosity and permeability tests with subsequent statistical result processing; as well as spectral analysis were used for the development of a catagenetic oil and gas occurrence model. The results obtained were compared with well logging data and confirmed by X-ray diffraction, fluorescent, bitumenological, and electron microscopy analyses.

The investigations allowed to establish laws governing the positions of abnormal interlayers in oil and gas occurrence columns; and confirm their correspondence with ancient oil-water contact (AOWC) stand locations. Higher concentrations of minor elements were identified in abnormal interlayers in the process of abnormal interlayer property investigation. The unique minor element profile of each AOWC allows to predict AOWC depths with a high degree of confidence, in order to avoid problems and accidents.

The lithogenetic occurrence models developed for the Orenburg and Karachaganak oil and gas condensate fields allowed to identify super reservoir development areas in columns, to develop recommendations concerning proper super reservoir penetration; to select optimal drilling conditions and fluids not damaging super reservoirs.

A method for AOWC area identification by higher concentrations of minor elements was developed; diagrams clearly showing metal concentration changes with the depth were constructed.

The feasibility of the method was confirmed. For example, for the Orenburg field, for which samples were taken from well 323 and spectral analysis of the samples was carried out, 17 super reservoir development areas were identified within the depth range of 1271.5-1814.5 m by the concentrations of metallic element complexes.

To prevent from drilling tool damage at the locations of these interlayers, a decrease in the drilling rate was provided for, which allowed to avoid accidents involving the drill bit and BHA components.

High minor element concentrations in gas-saturated occurrence part rocks are comparable with the concentrations of these elements in mineral ore deposits. Metals occur in the form of organoelemental compounds, metal salts inside intermolecular complexes. Mobile metal forms are associated with mobile phases of fluids, such as gas, light oil, and water. Low mobility forms enrich low mobility fluids, such as resins, asphaltenes, and hard bitumens. During operation, metals are accumulated in sediments down the hole, in well boreholes, on tubing and surface equipment. Investigation results allow to regard an oil and gas occurrence not only as a source of hydrocarbons, but also as raw material for the extraction of valuable metals in industrial quantities.

A method for preventing drilling accidents including well drilling using continuously changing drilling rates, core sampling and analysis for the presence of non-oil-and-water-soluble heavy metal compounds (Cu, Mn, Sr, Pb, V, Co, Bi, Ti, Ni, Ga), was developed. The presence of these compounds allows to determine the positions of super reservoirs in an occurrence; impurity quantities allow to determine rock hardness and the locations of hard interlayers which may cause accidents involving drilling tools, and to implement well accident prevention measures.