Communications: electrical – Wellbore telemetering or control – Selective control of subsurface equipment
Reexamination Certificate
2000-03-27
2002-11-12
Horabik, Michael (Department: 2735)
Communications: electrical
Wellbore telemetering or control
Selective control of subsurface equipment
C367S081000, C367S095000, C340S856400, C073S152160, C181S102000, C181S106000, C181S108000
Reexamination Certificate
active
06480118
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the drilling of subterranean wells. Particularly, this invention relates to methods and equipment for acoustically looking ahead of the drill bit, while the well is being drilled, e.g., one-hundred meters or more, analyzing and interpreting the data to identify and predict formation characteristics and properties of geologic features and structures within the planned drill path before being penetrated, and in response thereto, optimizing drilling procedures and equipment. More specifically, the “look ahead” information may be utilized to cost effectively maximize rate of penetration (ROP) and mechanical efficiency of the drilling system through use of more effective and efficient drill bits and related equipment. The result is improved ROP as compared to use of less efficient bits or equipment which otherwise likely would have been used and reduced risk of incurring unanticipated drilling hazards.
BACKGROUND OF THE INVENTION
When drilling subterranean wells, whether for hydrocarbons, water or other minerals, it is usually desirable to understand and obtain useful working knowledge of the formations, strata, environmental and hole conditions that may be encountered when drilling the wellbore. The more of this information that is available prior to actually encountering the change in formation or the drilling hazard, the more effectively the drilling plan may be designed and if needed, modified during drilling to provide a more cost effective response, efficiently drilled wellbore and safer drilling operation. The range of uncertainty in these conditions varies considerably from relatively low uncertainty in areas that have significant historical drilling data which may have been obtained from previous regional drilling experiences, to very high uncertainty in (a) exploratory wells, (b) wells in geologically complex formations, and (c) when drilling into previously unpenetrated horizons, such as when deepening a well. When drilling in areas of high uncertainty or risk the quality and quantity of useable information becomes more critical in optimizing the drilling program.
Techniques and equipment have been developed to gather and make available such information to improve drilling planning, efficiency and safety, including information gathered on both a macro and micro scale before the well is drilled and information gathered in real time, and while the well is being drilled. Room for improvement remains, however, in the quality, precision and timeliness of gathering and interpreting information so as to effect desirable improvements in a drilling program. Advances in measurement while drilling (MWD) equipment and seismic techniques are improving drilling efficiency and well quality, however, limitations remain which often result in economic and mechanical losses in drilling efficiency. Traditionally the vast majority of the information used in planning and drilling a well is obtained and analyzed prior to drilling. Once drilling has begun, relatively few changes are made in the drilling plan because the original plan is typically conservatively over-designed to account for reasonably anticipated but still unidentified drilling hazards, usually resulting in less than optimum ROP. One reason for this is that while drilling a well, relatively little additional information is gathered which may be useful in timely predicting unexpected changes in environment or formation characteristics before the changes are actually encountered. Unnecessarily accelerated bit wear or premature bit destruction may be avoided under prior art by employment of more mechanically conservative, less aggressive cutting bits.
Under the prior art it is difficult if not impossible to identify unexpected or previously unforeseen changes in geology, structure, stratigraphy, pore-pressure, rock matrix, faults, formation consolidation or other environmental alterations or hazards that the drill bit may encounter, with sufficient lead time before these events are actually experienced so as to timely implement prudent changes in the drilling program, including changing the bit selection. The inability to timely identify the presence and location of these formation changes may prevent improvement modifications in the drilling program, e.g., modifying bit selection, drill string and downhole assembly design, weight on bit, rotational speed (rpm) and determination of whether to rotate the drill string or “slide” drill utilizing a downhole motor. Failure to implement these and/or other modifications to the drilling program parameters often results in increased drilling time and costs through decreased ROP, a lower quality wellbore, less than optimal control of formation damage and decreased safety while drilling.
The prior art is incapable of fully effecting the desired improvements in optimizing the drilling program. The prior art is deficient in timely, precisely and confidently determining the numerous formation rock and pore properties which exist ahead of the bit in order to avoid excessive over-design of the drilling program. For example, it is generally accepted that in soft to medium-hard formations, polycrystalline diamond cutter (PDC) bits usually yield the best ROP. These bits are also among the more expensive. If an unexpected hard stringer or formation is encountered by a PDC bit, the PDC bit may be quickly destroyed or incur accelerated wear and damage. Thus, an improperly designed component in the drilling program, such as an improperly selected bit can result in excessive delays and costs, including rig time to pull the pipe out of the hole (trip), change bits and run the pipe back to bottom. Pieces of the destroyed bit may also have to be “fished” out of the hole before drilling may be continued, thereby resulting in additional “trips” and significant costs.
An additional important parameter in controlling well costs and well quality is pore pressure determination. Identification of the presence of over-pressured or under-pressured zones should be made before they are encountered by the bit. Over-pressured zones can result in loss of well control, potentially leading to loss of the well, the drill-string, the drilling rig and possibly human life. Under-pressured zones can result in loss of costly drilling fluid, formation damage, loss of well control, stuck pipe and loss of the drill string or the well.
Proper planning is important in avoiding drilling hazards in the most cost-effective manner and in maximizing drilling ROP efficiency. Proper planning, however, requires timely, sufficiently detailed, useable information. Historically, an over-designed drilling plan and inflated equipment safety factors are typically built into a well plan to mitigate the effects of unforeseen hazards, often resulting in excessive and usually significant additional costs. Timely, useable information is valuable in optimizing a drilling program and the advantages may be reflected throughout the many costs included in drilling a well.
Techniques are known which use acoustic signals to gather and process data while drilling that relate to either recently drilled formations or undrilled formations within close proximity of the drill bit or to information pertaining to the drill string and downhole conditions thereof. One common technique is to gather three-dimensional seismic data at the surface or at sea before drilling the well in an attempt to map and identify relatively significant subsurface features, as disclosed for example in U.S. Pat. No. 5,555,531. This method may also include preparing high resolution three-dimensional vertical profiles from the data, preparing an artificially-illuminated and rendered surface based on the data, potentially identifying significant reflective sub-surface features, including those which may be hazardous. However, with increasing depth of investigation these seismic methods may suffer decreasing resolution and cumulatively increasing error. In addition, although seismic while drilling techniques are known, seismic is typically
Browning & Bushman P.C.
Horabik Michael
Wong Albert K.
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