As fields mature, drilling can become more difficult. The likelihood of losses increases as reservoir pressures decline while higher mud weights are needed to prevent collapse of overburden shales as targets are pushed further from the platform. Drilling parameters for the Forties field have become fairly well established after years of experience yet 65% of the wells drilled between 2002 and 2007 experienced incidents attributed to instability. As field production declined, economic viability demanded a step change in performance.
Through a better understanding of the field geomechanics and past drilling events, the Apache drilling team has implemented fit for purpose drilling procedures that have significantly improved drilling efficiency.
This paper describes how geomechanics analysis has been used to assist well planning. Incorporating the experience of recent wells, the Forties mechanical earth model has been refined and provides key inputs needed to optimise well plans and adapt drilling practices to changing conditions.
The adverse effects of anisotropy is a key reason for wellbore instability in the overburden. A joint Apache-Schlumberger team has been working to integrate geomechanics and geophysics knowledge of the field to quantify the effects of anisotropy related to bedding planes and weak shales.
It can be difficult to predict drilling and completion risks during well planning, often due to the lack of distinction between events caused by formation instability and those which are drilling induced (drilling practices, hole cleaning). Capturing and classifying historic drilling events is a fundamental key process in understanding the mechanism and causes of well bore failures.
Drilling performance in this mature field has been improved through the collaborative effort of Apache staff and key service providers. The refinement of the wellbore stability model has enabled sound practices and procedures to be developed.
This study aims to assess the concentrations of natural radionuclides activity (226Ra,232Th and 40K) and calculate a number of radiation risk indicators in some types of field crops in different areas of Tikrit City - Salah Al-Din Governorate - Iraq. The measurement was carried out using a gamma ray spectroscopy connected with a scintillation detector crystallized with thallium-activated sodium iodide NaI(TI). The results were that t 0……he mean concentrations of elements (226Ra,232Th and 40K) wer (6.79±0.33 1Bq/Kg,10.79 ± 0.640 Bq/Kg, 133.34± 5.895 Bq/Kg), respectively. And the radiation risk indicators were less than the international permissible and the recommended average, so that the samples under study are safe and suitable for human and animal consumption.
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