Advancements in Subsurface Core Sampling with Drilling Core Bits: Techniques and Innovations in Oilfield Analysis

Oil is buried in pCoring Bitsorous and fractured rock formations underground. Petroleum engineers always aim to extract core samples containing oil and gas from the subsurface to understand the true nature of the reservoir. Currently, there are two main methods for obtaining subsurface core samples: perforation coring and drilling coring. Perforation coring, which involves lowering a limited number of sporadic core samples on a cable, has limitations such as small volumes and sporadic sampling, making geological analysis challenging. To analyze subsurface formations and oil sands effectively, conventional drilling coring methods are widely used.

During drilling coring, a specially designed coring bit is added to the coring tool at the bottom of the drill string. The coring bit, under the combined action of vertical load and torque, crushes the rock at the wellbore and retains a cylindrical core sample within a core barrel. After drilling to a specific depth, the coring bit is separated from the core sample using a method that matches the tool, and the core sample, along with the coring tool, is retrieved to the surface. This drilling coring technique allows for a comprehensive range of geological analyses and tests on the core samples, which are crucial for understanding the lithology, properties, and reservoir evaluation of underground formations.

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At present, drilling coring can be categorized into conventional drilling coring and special drilling coring. The former includes short, medium, and long core barrel coring, while the latter includes directional coring, horizontal well coring, sealed coring, pressure-maintaining coring, and shape-preserving frozen coring, among others. The development of drilling coring technology in China has been rapid, with the country's technology level largely synchronized with international standards. In the 1960s to 1970s, oilfields like Daqing, Shengli, and Dagang set world records for drilling long core barrel samples, with a maximum length of 145.42 meters. In the 1980s, conventional drilling coring technology in China approached international standards. In the 1990s, China reached international advanced levels in developing tools for coring shallow, loose, and unconsolidated formations, as well as for drilling sealed coring tools.