
	2021		2020

	(In millions)
Exploration and Production
Unproved properties	$	184	$	164
Proved properties	2,877		2,930
Wells, equipment and related facilities	23,745		23,224
	26,806		26,318
Midstream	4,342		4,163
Corporate and Other	30		38
Total — at cost	31,178		30,519
Less: Reserves for depreciation, depletion, amortization and lease impairment	16,996		16,404
Property, Plant and Equipment — Net	$	14,182	$	14,115

Capitalized Exploratory Well Costs: The following table discloses the amount of capitalized exploratory well costs pending determination of proved reserves at December 31 and the changes therein during the respective years:


	2021		2020		2019

	(In millions)
Balance at January 1	$	459	$	584	$	418
Additions to capitalized exploratory well costs pending the determination of proved reserves	222		111		224
Reclassifications to wells, facilities and equipment based on the determination of proved reserves	—		(111)		(58)
Capitalized exploratory well costs charged to expense	—		(125)		—

Balance at December 31	$	681	$	459	$	584
Number of Wells at December 31	35		22		31

During the three years ended December 31, 2021, additions to capitalized exploratory well costs primarily related to drilling at the Stabroek Block, offshore Guyana. In 2019, other drilling activity included the Esox prospect in the Gulf of Mexico.

Reclassifications to wells, facilities and equipment based on the determination of proved reserves in 2020 resulted from sanctions of the Payara Field development, the third sanctioned project on the Stabroek Block, offshore Guyana, and an additional phase of development at the North Malay Basin, offshore Peninsular Malaysia. In 2019, reclassifications to wells, facilities and equipment resulted from sanction of the Liza Phase 2 development on the Stabroek Block and the Esox tieback well to the Tubular Bells Field in the Gulf of Mexico.

Capitalized exploratory well costs charged to expense in 2020 of $125 million primarily related to the northern portion of the Shenzi Field (Hess 28%) in the Gulf of Mexico due to reprioritization of our forward capital program in response to the significant decline in crude oil prices. The preceding table excludes well costs incurred and expensed during 2021 of $11 million (2020: $67 million; 2019: $49 million).

Exploratory well costs capitalized for greater than one year following completion of drilling were $459 million at December 31, 2021, separated by year of completion as follows (in millions):

Guyana: Approximately 90% of the capitalized well costs in excess of one year relate to successful exploration wells where hydrocarbons were encountered on the Stabroek Block (Hess 30%). In the fourth quarter of 2021, the operator submitted a fourth development plan for the Yellowtail Field to the Government of Guyana for approval. The operator also plans further appraisal drilling and is conducting pre-development planning for additional phases of development.

JDA: Approximately 8% of the capitalized well costs in excess of one year relates to the JDA (Hess 50%) in the Gulf of Thailand, where hydrocarbons were encountered in three successful exploration wells drilled in the western part of Block A-18. The operator has submitted a development plan concept to the regulator to facilitate ongoing commercial negotiations for an extension of the existing gas sales contract to include development of the western part of the Block.

Malaysia: Approximately 2% of the capitalized well costs in excess of one year relates to North Malay Basin (Hess 50%), offshore Peninsular Malaysia, where hydrocarbons were encountered in one successful exploration well. Subsurface evaluation and pre-development studies are ongoing.